This post originally appeared on the Nylon Calculus on 7/23/2014. Re-posted here to keep all of my Celtics posts together.
Also see my other posts there on the Value of Free Throws and the Spurs Draft Prowess.
The Celtics seem to have signed Evan Turner as a free agent, probably not the number two pick most of the tank commanders were hoping for at the beginning of last year.
Reports are that this is just part of the mid-level exception, and likely a short term contract, so the money is not a concern. But the Turner signing brings the Celtics to 15 players with guaranteed money and that much closer to the tax line, limiting some flexibility and squeezing out the three non-guaranteed players under contract, most notably Christapher Johnson.
It is hard to tell at this point whether the Turner signing makes further trades more or less likely. On the one hand, as I noted, roster and financial flexibility are somewhat more restricted, on the other hand the roster may make even less sense than it did, so trades seem more likely. Given that, I decided to take a look at Turner in the context of the current Celtics lineup, to see how he might or might not fit, which can also shed light on the trade question.
Turner can play either shooting guard or small forward. Last year according to 82 Games, Turner played almost 75% of his minutes as a small forward, while his Indiana playing time was more evenly split. On this current roster I think Turner probably gets more time at small forward, especially if they are serious about playing Marcus Smart off the ball.
Here is how Turner compares to the Celtics' current small forwards using some of the advanced overall metrics, color formatted to show the relative strength:
Essentially the 31 year old Gerald Wallace is the only one to rate as above average in any of the metrics — Win Produced and RPM. Otherwise it isn't pretty and Turner is pulling out a lot of red, even in that group. So, the overalls on Turner aren't good last year, nor were they much better in previous seasons.
But, let's brave some of the finer grained numbers to see what kind of a game Turner has, or maybe could have. Turner tends to be a ball-dominant wing, which shows up in his distribution numbers. He got both more assists and had more turnovers than the other current small forwards on the Celtics roster. His overall assist-to-turnover ratio is approximately average for a small forward, if we're generous.[1. Per Basketball Reference player comparison] 
Both Green and Johnson tend to play off the ball more than Turner or Wallace. Turner looks like an adequate secondary ball handler.
I have been re-working a cluster analysis of players by their shot selection types that I ran last year using the unfortunately now shut down HoopData site, this time using NBA.com data (which one expects to be around for a while). The final analysis is still a ways off, but both in the prior analysis and the new version Turner rated as a 'Slash' wing relying more on driving or cutting to the rim than the three pointer. Unfortunately, he too often settled for pull-up mid-range shots when he was cut off from the basket, putting him in a possible third category of Mid Range shooters. As seen in this shot chart created by Austin Clemens:
Looking at the chart, not only is there too much blue, but too much below-average shooting in below-average places. There is a similar pattern viewing his shooting in tabular data along with the other Celtics small forwards the pattern is just as clear[2. Ibid.]:
The funny thing is that Turner actually shot fewer mid-range shots last year than any previous year. Unfortunately, progress has been slow and mostly offset by a fall in his conversions at the rim. His free throw rate is also poor for a Slashing guard, though that too had a slight uptick, especially in his Indiana stint.
Obviously there's an argument for the mid-range game if a player is good at those shots like Dirk Nowitski. Turner is not, see above.
By the way, it is also clear looking at this that Chris Johnson fills a different role offensively than the other wings on the roster. He is the only true stretch player and one that mostly plays off of the ball.
In the other stats, Turner is a good rebounder for his position, though mostly in less valuable defensive rebounds, barely registers on blocks and is below average on steals.
The argument has been made that the Celtics might expect Brad Stevens to transform Turner into an asset the way he did with Jordan Crawford last year. That doesn't really seem like the best use of Steven's time given the two first round picks on this roster and Kelly Olynyk and Jared Sullinger still in need of development.
It's hard to see the precise role Turner could fill on this roster even with improvement other than secondary ball handler off the bench, which makes more moves feel all the more likely.
