This defense is so... regressing?

The Mariners defense as rated by Plus/Minus reached a low point near the end of May, standing at 36 plays below average through May 26, 52 games into the season. It put the team on pace to finish the season at 112 plays below average, a remarkable 90 runs below average. 90 runs. You know how much 90 runs is?

If we went back in time to 2007 and replaced the bats (ignoring defense) of our middle infield combo of Lopez and Betancourt with the bats (ignoring defense) of Robinson Cano and Hanley Ramirez, you still wouldn't quite get 90 runs of difference. 90 runs is a lot of funking runs.

I noted earlier this month that the defense had been better since that point, slowing the rate of separation from league average and pointing out that it somewhat coincided with Reed's introduction to regular play.

However, we now stand 99 games in and the Mariners team defense, rated by Plus/Minus doesn't sit at -69 as it were if it had kept pace. Instead, it sits at -25, an actual improvement over past numbers. According to Plus/Minus, since May 26th, our defense has been 11 plays above average. That cannot possibly be correct right?

Well, a quick check of team BABIP by month suggests it is. The Mariner pitchers suffered a BABIP of .324 in the month of May after a .298 BABIP April. June saw the team regress back toward that league mean with a .304 number and so far in July they're posting a .274 BABIP number, far better than average.

As to what weights to assign to new personnel and general regression for this improvement I can only speculate, but glancing at the position-by-position figures, it does appear that Yuni has gotten a little better and Miguel Cairo has been a substantial improvement over Sexson at first. Meanwhile, Reed is gobbling up balls like Ms. Pac-Man does 2D dots... or something.

Remarkably, the Ms outfield now rates rather neutral according to Plus/Minus with the majority of the -25 plays coming from the infield. It will certainly be worth watching as this season becomes more and more of a showcase for 2009.