Okay, so the headline is a little bit reductive. But for those who believe in John Hollinger’s PER statistic, that’s precisely what happened yesterday when the Phoenix Mercury traded Temeka Johnson straight up for Andrea Riley of the Tulsa Shock. Of the 121 players who appeared for at least 150 minutes in the WNBA last season, Riley rated 118th. And for those who’ve read my columns over the last year or two, you’ll be aware that 118th might actually be slightly higher than I’d rank her. So what on Earth possessed the Mercury to make this move?

In fairness to Phoenix, Johnson hasn’t exactly been lighting it up herself for the last couple of years. After arriving as Kelly Miller’s replacement in 2009 and playing her part in the charge to a championship, TJ’s effectiveness has diminished in the last two seasons. While she retained her starting spot, she was often sat on the bench in crunch time when head coach Corey Gaines went to bigger lineups, and her scoring average dropped three full points to only six per game in 2011. And that’s before we even consider her matador brand of defense, which occasionally stood out even among the deplorable Mercury team defense as especially poor. However, her shooting averages have remained pretty decent, especially compared to the likes of Ketia Swanier and Alexis Gray-Lawson who were coming off the bench behind her. Plus Johnson was always a veteran option who knew what her coach wanted and how the team was supposed to be playing on the floor. Search back a couple of years and you’ll read a swathe of comments from the likes of Diana Taurasi and Cappie Pondexter about how much they loved playing with a true point guard who knew how and when to get them the ball. Johnson’s game really hasn’t changed much since then – the roster’s simply weakened around her while their competition has improved.

Don’t expect many comments from Mercury players about Riley’s ‘true point guard’ skills in 2012. If she even makes the roster. Riley’s a gunner with no conscience. In 2010 in LA and 2011 in Tulsa combined, she’s jacked up an extraordinary 32 shots from 26 feet or deeper (that’s five feet or more beyond the three-point line) – second only to Tina Thompson. In fact, at one stage last season I compared her to new teammate Diana Taurasi, who also has a tendency to pull up from seriously deep and fire whenever she sees fit. Except that there’s one key difference – Riley can’t shoot (there are plenty of other differences too, but let’s start with that one). We hear it over and over again from commentators and analysts who watched her in college, that Riley can get hot and hurt opponents, but I’m not sure how much evidence they want at the pro level that she repeatedly takes horrendous shots and very few of them go in. She’s a 31% shooter over her first two years in the WNBA, 24% from three-point range, and she shoots about 1.5 free throws a game (so she’s not making up for anything at the line). She often pounds the ball into the ground at the top of the arc, killing the shot clock, before deciding to simply toss up a brick – but there are plenty of possessions where she just fires away early on without even trying to run an offense. It’s ugly. She is quick, you have to give her that, and at times she can break down a defense off the dribble, but it’s rare and she doesn’t really know what to do once she makes it into the paint. You’re just as likely to see a painful turnover as you are to see her find an open teammate. Outside of it being embarrassing to cut the player you traded your starting point guard for, it honestly wouldn’t be a surprise to see her waived in training camp. Both Swanier and Gray-Lawson have looked better players during their time in the WNBA. Although by the way, one of those three players whose PER rated below Riley in 2011? Ketia Swanier.

So here’s the upside for Mercury fans: cash money, baby. As with the Seattle trade a couple of weeks ago, this trade creates cap space for a team that was perilously close to the limit at certain stages of last season. Johnson is practically a max player (around $100,000) while Riley is still on her rookie-scale contract (and would be overpaid in 2012 at $47,561), so this switch gives Phoenix some extra room to pursue free agents in the upcoming window. If they needed the space, and have actual plans to use it, then by the time the 2012 season starts this trade could make more sense. We’ll see. At the same time, the cap’s gone up again this year; the Mercury already dumped Kara Braxton and her max-deal during the 2011 season; and Marie Ferdinand-Harris’s overpriced one-year deal has expired. So did they need the extra room? They’ve got four high-priced players left on this roster, including Penny Taylor (who may or may not play the whole season in 2012) and Nakia Sanford (who’s in the last year of her deal). They have players like Swanier, Gray-Lawson and maybe Ferdinand-Harris to re-sign (assuming they want to keep them), and they’re one year away from having to pay DeWanna Bonner proper money, but this still looks premature and unnecessary. If the cap room brings them someone unlikely like Sue Bird, Tanisha Wright, Candice Wiggins or even Ticha Penicheiro, then okay. If it ends up going to a Miller twin or two, then it makes you wonder why they bothered. If they spend it on no one, then you have to think they’re tightening the purse-strings and/or thinking about the potential Griner/Delle Donne/Diggins draft in 2012.

As for Tulsa, this makes all kinds of sense. Johnson may be expensive for what she produces, but she’s a proven veteran who can give the Shock something resembling a steady hand at the point. She also has a history of stepping up her game in her first year in a new city (as a rookie in Washington, and after trades to LA and Phoenix), so they’ll be hoping to see that again in Tulsa in 2012. New head coach Gary Kloppenburg already had Ivory Latta, but this strengthens a key position on the floor, especially necessary for a team that often looked disorganised and sloppy last season. Also, the Shock have acres of cap room but are likely to find it hard to attract top-end free agents, so making deals like this is their best way of improving the roster. They simply need more talent wherever they can find it, and this switch is a definite upgrade. And having advocated simply cutting Riley on several occasions last season, it’s addition by subtraction even if Johnson’s a bust.

Phoenix: F  Sorry, they just acquired one of my least favourite players in the league straight up for a starter. I can’t honestly go higher.

Phoenix (if you want to be generous): Incomplete  Maybe they needed the extra 50 grand of space. Maybe Bird, Wiggins and Langhorne are all on their way. We’ll see.

Tulsa: A  Can’t argue with Coach Klopp’s first move. Dump Riley, add a veteran point, and upgrade your talent level. Even the mediocre TJ from the last year or two would help his team.

Temeka Johnson: C  She looked like she could use a new start for much of last season, but you can’t ignore that she’s going from a Western Conference finalist to a team with a lot of holes. It’s a long-term project in Tulsa, and she might be gone before the turnaround gathers much steam.