Skylar Diggins, Bria Hartley, and the developmental trajectory of rookies

We've already discussed Tulsa Shock guard Skylar Diggins' remarkable improvement in her second year as a pro, but there's also a bit more to be said about that leap and what we can learn about player development generally in the league and for the trajectory of draft prospects as well (before we begin thinking more specifically about the 2015 WNBA Draft).

First, she provides a direct challenge to the commonly held belief that players need to go overseas if they wish to improve during the WNBA's lengthy offseason (independent of financial concerns) - strength was one of her most obvious problems in her rookie year, she worked on it during the offseason and she made herself into an All-Star starter. Whether that is the best path to improvement for everyone is another discussion, but it makes it a lot harder to criticize other players for not going overseas in the future.

But second, and perhaps more interesting as applied to other players, Diggins is a quintessential example of why we should value demonstrated strengths over overall performance when considering the potential of young players, whether talking about rookies or college prospects. Although this is an issue I've explored in the past, the last two drafts - with Diggins being the prime example - have really helped to solidify a few points about what things are most important statistically.

We've been through this equation before, but a WNBA player who has a poor rookie season could legitimately say, "I had a bad stretch of 34 games" without being considered delusional: that is almost the story of NBA superstar Kevin Durant, who had a bad stretch of 45 games to begin his career. Although Durant might be the clearest and most prominent example of that in the NBA, it's just a fact of life in basketball: you really can't draw hard conclusions from 34 games of a rookie year given all they have to learn and the adjustments they have to make coming from college ball (a transition that is far more pronounced in the WNBA). And in many ways, Diggins was worse than Durant was in that first stretch of his rookie year - Durant was younger, had excellent size for his position and was a more efficient scorer.

But there's something subtle in that story of Diggins' first year that might have gotten glossed over in fawning over her second year improvement: in reviewing Diggins' rookie season last year, I wrote, "Diggins has shown flashes of being elite...Patience is the key with Diggins." Although that was at least partially a justification for putting her on the All-Rookie team despite a poor rookie season, there was actually more to it: the importance of showing signs of any sort of elite strength, even during a generally poor season.

The lesson of Skylar Diggins' turnaround

As I ran through briefly back then, Diggins' rookie year was like a scattered puzzle of tools that she just never really brought together consistently or during one solid stretch. But one thing did stand out as promising by the end of the season, despite all the talk about how much she struggled to adjust to the pros: Diggins finished ninth in the league in assist percentage, according to Basketball-Reference, along with the third-highest usage rate of any starting point guard in the league (21.7%). Her free throw rate of 33.2% was outstanding for a point guard, suggesting along with the other two marks that she had the potential to create plays as a scorer off the dribble as well. Although she wasn't particularly good at finishing plays as a scorer, she showed signs of being elite at creating them and that justified finding hope in otherwise dismal circumstances.

That ability for both Diggins and Durant to create plays - for either themselves or others - reflects why Bradford Doolittle of Basketball Prospectus once described usage rate as "the most underrated metrics in basketball" when discussing Durant's rookie year back in 2008. Diggins' usage rate wasn't extremely high -- to the point of it being high among point guards, the nature of running an offense demands doing things that don't always produce a counting stat -- but the general principle about being able to create plays still applies: by "simply" adding strength and refining her skills (and having less of a promotional circus around her off the court), Diggins was able to bring those disjointed tools together for a spectacular All-WNBA caliber second year.

The statistical argument for Diggins as Most Improved Player is a matter of vastly improved efficiency, obviously meaning it was very low after her first season. Although I used PER to describe that improvement in that previous piece for the sake of simplicity, Valuable Contributions Ratio is my preferred metric because it does a better job of balancing usage and efficiency in the context of an individual's contribution to their team while they're on the floor. I still like the World of Warcraft effective damage per second analogy (h/t Shannon), but in short it's about measuring the contribution a player makes to their team proportionally in the minutes they were given - in plain terms, it rewards players who do a lot of good in low minutes and penalizes players who earned a lot of minutes but had a lower "work rate" or have higher averages because they had more time to produce.

Diggins' disappointing rookie season produced a VCR of .66, well below average for any player in any season (.75-.85 in recent years with fluctuating numbers of players and teams) and not even in the top 10 last season among rookies. Nevertheless, the very fact of earning minutes was as important as any sort of strength she showed: she wasn't especially impactful in those minutes, but there just weren't many rookies last year who even earned that many minutes to begin with. That she had those flashes of brilliance just showed that she might have something to build on.

One basic analytics lesson of Diggins' huge turnaround is that numbers can be used to find reason for either hope or condemnation - they're indicators of performance that we interpret rather than firm statements of innate qualities. And as we accumulate more data, we're able to use them to better project where a player might go without necessarily making that projection as a statement of fate.

In other words, it's fancy guesswork grounded in evidence-based assumptions gleaned from patterns in performance because we can't predict coaching, work ethic, system, etc.

Bria Hartley's uneven rookie season

I rehashed the Diggins story because I think it lays the groundwork for understanding the performance of a rookie I'm struggling to get a handle from the 2014 class: Washington Mystics rookie Bria Hartley, who also made the All-Rookie team after earning a starting spot and more minutes than most of her peers.

As Pat has mentioned previously, Hartley was actually better than Diggins in multiple ways as a rookie, whether you look at PER, various other performance metrics or account for differences in how much they handled the ball. They are also remarkably similar in a number of ways.

Player	Year	Tm	G	MP	USG%	TS%	FTr	3PAr	ORB%	TRB%	AST%	STL%	TOV%	PER	ORtg	DRtg	WS/48
Diggins, Skylar	2013	TUL	32	845	21.7	0.44	0.33	0.29	2	4.3	26.4	2.6	22.9	9.8	85	106	-0.04
Hartley, Bria	2014	WAS	34	924	21.8	0.48	0.27	0.33	2.5	4.6	20.6	1.4	19.9	10.1	91	103	0.03

Rookie year statistics for Skylar Diggins and Bria Hartley (via Basketball-Reference).

Right away, we can see that neither player was a particularly efficient scorer as a rookie - both were inefficient scorers at almost exactly the same usage percentage and Diggins' true shooting percentage was given a boost by her ability to get to the free throw line while Hartley took and made more threes to help her efficiency. But both were essentially inefficient combo guards in their rookie years: even if Hartley was better, both were below average players.

But where they really diverge is when you start to look for an elite strength: for everything else that went wrong, the combination of Diggins' assist percentage, free throw rate, and usage rate was still reflected an elite playmaking strength. In contrast, it's hard to say that Hartley was either elite or efficient at any one thing -- she rates as a combo guard just as Diggins did in her first year, but she swings far closer to the scorer than distributor end of that spectrum. And what initially caught my eye was that Hartley finished the regular season with a VCR of .63, lower than Diggins' rookie season rating, not in the top 10 of this season's rookies and closer to a point where you might start to wonder how much upside a player has (if you're looking for reasons for that, the lacking assists, steals, and made shots in more minutes did matter in addition to the turnovers).

Still, beyond the numbers, it's a little unfair to compare Hartley directly to Diggins, who was also more heavily responsible for lead ball handling duties. Hartley was involved in making plays in a point guard role, but was not particularly adept at it, played on a team that was stunningly balanced in how they distributed touches (which lessens the burden on ball handlers) and was better off the ball in college.

So that leads to another question: are there other players who bounced back from a similarly poor rookie year to emerge as significant contributors later in their careers? Yes, but Diggins is still probably the most similar scenario.

Player	Year	VCR	USG%	Ast%	PPR	TS%
Bria Hartley	2014	0.63	21.78	20.4	-1.66	48.5
Skylar Diggins	2013	0.66	21.7	26.4	0.11	43.8
Courtney Vandersloot	2011	0.61	19.1	28.2	-0.94	46.7
Monica Wright	2010	0.68	23.8	11.1	-3.88	45.81
Essence Carson	2008	0.69	21.4	9.3	-2.21	42.02

Statistics for rookie guards with VCRs under 0.70 (USG%, Ast%, TS% via Basketball-Reference).

Vandersloot is also a point guard, but the thing that really stands out about every one of these players is that they had elite strengths underlying those poor VCRs.

Vandersloot showed potential to become an elite distributor with added strength and currently has one of the top five assist percentages of all-time (right behind Sue Bird, who she was compared to once or twice as a Washington native). Both Carson and Wright made names for themselves in college as defensive players and have brought that to their teams as pros. Although neither was quite the rookie ball handler that Hartley was, both had better developed mid-range games and both took at least two more seasons to become productive contributors...before declining in about the same time as they rose.

But the point is that while all of those players had some sort of potentially elite skill, it's still not clear what Hartley's is: her rookie season sits in a weird space of neither showing terrible weaknesses nor exceptional strengths.

Hartley was better than Carson or Wright at finishing within five feet during her rookie season, but still rated as somewhat mediocre (54%) compared to players with 100+ attempts this season. She was a better 3-point shooter than any of the guards above, but is still about average. She's the most efficient scorer of that group overall but a 48% true shooting percentage isn't outstanding. She's a more efficient rookie ball handler than Carson or Wright - and obviously has handles - but can't (yet) be considered a solution at point guard with a low assist ratio, pure point rating, and scoring efficiency. Looking at her monthly splits, those key numbers remained relatively stable for Hartley: the lone bright spot was an improving 3-point percentage, which plays to her college strength of spot-up shooting.

Looking forward with an open mind

Unfortunately, those numbers reflect the basis for one of the major questions about Hartley as a prospect: "How well will Hartley score against WNBA defenders in the halfcourt?" And, related, how effective will she be as a distributor if she doesn't score efficiently?

Hartley had one major red flag as a prospect that has fairly consistently hurt players coming into the league: she had a high 3-point rate and low free throw rate, normally indicative of a player who's not adept at creating her own shot. In short - and this applies to the 2015 draft quite directly -- volume 3-point shooters don't make much impact in the league. Working in Hartley's favor was that she was also an efficient ball handler - not common for that type of volume 3-point shooter - but we essentially saw the limits of those college tendencies in her rookie season in the form of those so-so usage and efficiency numbers.

Just to be totally clear, Hartley is by no means a "bad" player.  There's a major difference between saying someone doesn't have an elite skill and that they have no demonstrated skill - there are plenty of players in the latter category who have managed to gain favor in the league and Hartley isn't one of them. But the early conclusion for Hartley still remains that she projects as a scoring role player, perhaps best in a Sixth Woman position for a successful team like Wright has grown into - for the most part, the players that overcame poor rookie years to become more than that offered more reason for optimism early on.

But to the point about Diggins, what we can't quantify about Hartley -- and part of what made her difficult to get a handle of as a draft prospect -- is how much this offseason experience with USA Basketball will help her down the road and whether she'll be able to make incremental improvements across the board to become a well-rounded combo guard.

If nothing else, Skylar Diggins has taught us that a smart offseason program can do wonders after 34 difficult games.