He's had a renaissance at age 33. Many of us would like him back, not just for the bat but because his positional versatility makes our bench play much longer.
I wanted to take a look at the elements of his 2015 renaissance to form a judgement about how much is flukish and how much has a chance of being sustained into next year.
There has been a certain amount of research done on how quickly certain stats stabilize. The more slowly they stabilize the more likely they are to be flukes or misleading in small samples.
For the stats I want to look at the rough order of speed of stabilization is: strikeout rate, walk rate, ISO and BABIP. BABIP stabilizes much more slowly than the other three.
I'll start with KJ's strikeout rate since the research indicates that a change there is most likely to be meaningful. In 2012-2014, he put up strikeout rates of 27.4%, 24.3% and 23.9%. This year it is at 20.6%. The improvement here is quite encouraging. A 20% strikeout rate is not great unless you are a slugger. But it gives you a much better chance of success than a 25% strikeout rate.
His walk rates for 2012-2014 were 10.7%, 8.6% and 9.8%. This year it is 6.3%. So a negative development. But it doesn't fully offset the improvement in the strikeout rate. First the improvement in the strikeout rate is larger. And remember that strikeout rates stabilize faster than walk rates for hitters, so this makes the strikeout rate improvement more meaningful.
Let's look at ISO now. His 2012-2014 numbers were .140, .175 and .147. This year it is .183. That's quite a nice improvement, especially when you consider he played in better hitters' parks in 2012-2014. At the same time you have to discount some of it.
The number you discount a lot of is BABIP if it shows a big change from the prior baseline. His 2012-2014 BABIP numbers were .292, .276 and .266. This year it is at .313. Digging a little deeper we see that his line drive rate in 2012-2014 was 21.0%, 15.2 and 21.1%. This year it is 25.5%. Line drive rate stabilizes fairly quickly. So some of the improvement in BABIP is real and sustainable (maybe as much as half). But the rest is not, which means that realistically we should expect his BABIP to drop to 20-30 points going forward.
So what is the bottom line. In trying to decide what kind of performance he would give us next year, I would bank on most of the changes in his strikeout, walk and ISO rates being sustained. But would discount at least 20 points off his current BABIP. That's good enough to make me want to bring him back.
He and his family live in the area. He's talked about how nice it has been to be able to spend more time with his kids during the season. I think he would like to come back and would likely accept a little less than from other teams to be able to do so. At the same time, he's earned a raise from what he's making this year (1.5M).