The Not-So-Secret Weapon of Sergio Santos

2013 was a year with a great deal of surprises for Blue Jays fans. Unfortunately, very few of those surprises were of the pleasant variety. In fact, it would probably be fair to describe the season as a whole as an unpleasant surprise. However, even within the depressing black hole that was last season there were a few joyful revelations regarding some of the players on this team. Dustin McGowan made more than a cameo appearance, Colby Rasmus was excellent, and Edwin Encarnacion showed that the gains he made in 2012 were sustainable and managed to grow as a player by seemingly deciding that striking out was something he no longer felt like doing. One of the pleasant surprises that has been discussed relatively infrequently in the context of the last year's disaster was Sergio Santos's season.

It would be unfair to call the season Sergio Santos had an unmitigated success due to the fact he logged only 25.2 innings, but when he did see the field he was pretty incredible. Here's a review of what he did in limited work last season:

The .175 BABIP is ludicrously low and it's hard to see a 4.2% HR/FB rate holding up at the Rogers Centre in 2014, so the xFIP is likely the most reliable indicator here. That being said, a 2.61 xFIP is pretty impressive. Perhaps the most worthwhile gain here is the way that Sergio Santos cut down on his walks from a career BB/9 rate of 3.89 to a fairly minuscule 1.40. In a sample this small a great deal can happen and mean absolutely nothing, but Santos demonstrated pinpoint control for the first time in his career last season. For a guy who is fairly new to pitching, in the scheme of things, that's fairly encouraging.

When examining a small sample looking at the results will rarely yield many answers we can trust, but looking at change in approach can be far more enlightening. Luckily for us, it appears that Sergio Santos made such a change last year. If we re-examine Santos's improved control numbers we can find out the origin of this improved control. Essentially, there are two reliable ways to throw more strikes. You can throw the ball in the zone more or you can have guys swing at your pitches outside the zone more. It's also conceivable to get the umpire to call a lot more of your balls as strikes, but you need a significant catching change to a superlative pitch framer for that to come into the equation in a truly meaningful way. If we assume that in order to cut his walk rate Santos had to get more swings out of the zone or put his pitches in the zone more consistently a look at his PITCHf/x plate discipline numbers shows which of the two was a more significant factor:

It seems apparent that the root of Santos's ability to cut down on his walks in 2013 was an improved ability to get batters to chase out of the zone. That makes us ask how he managed to accomplish that. The answer to that question lies in his pitch selection, which changed significantly in 2013:

Santos leaned on slider more than ever before last year, which is significant because when it comes to getting guys to chase out of the zone his slider is a pretty unbelievable tool. The following Brooks Baseball zone profile shows hitters' swing rate against Santos's slider and as you can see hitters chase out of the zone with impunity:

Moreover, when they do decide to swing they are consistently coming up empty. Notice the low and away quadrant to right-handed hitters in the following zone profile depicting batters' whiffs per swing against the slider:

That picture shows a pitch that is ridiculously effective. More often than not when writers use words like "ridiculously" there is some degree of hyperbole but the slider of Sergio Santos is really, truly, ridiculous.

What we have here is a situation where a pitcher is leaning more heavily on his best pitch and having a great deal of success. Seems fairly normal, seems fairly intuitive, and seems like it's a good idea. However, unfortunately it's a little more complicated than that. There is evidence to suggest that sliders put additional stress on pitchers' arms and can make them more likely to spend so time on the disabled list. In fact, in Jeff Zimmerman's yearly DL% predictions he includes pitchers that throw sliders 30% of time or more in a special high-risk category.

Injury predictions are far from an exact science and every pitcher is different, but it's possible that Sergio Santos is putting his arm at additional risk by his very heavy usage of his admittedly unbelievable slider. Given that Santos has managed to pitch just 30.2 innings in his two seasons with the Blue Jays due to an onslaught of injuries he's not the type of guy who can afford to be taking risks with his arm. There is no definitive way to say that Sergio Santos will get injured or stay healthy, but this is a situation where a known injury risk might be further decreasing his chances of staying off the DL with his approach. The slider intensive approach definitely worked for Santos in 2013 but it is a scary one going forward.

When you've got a weapon like the slider in Sergio Santos's arsenal it's hard to resist turning to it as often as humanly possible. However, such a strategy might not be in the Blue Jays setup man's best interests going forward. If Santos continues with the approach that made him an elite reliever,albeit in a limited sample, in 2013 Blue Jays fans may well end up seeing something similar in 2014: a small quantity of brilliant innings.