Hector Santiago is nipping on the heels of Anibal Sanchez when it comes to Homeruns allowed per 9 innings. Sanchez sits at 2.22 while Santiago is at a career high 2.04 (for comparison, Jered Weaver is 1.85 and Jake Arrieta is .36). In fact, since Santiago's first full season, he has been trending upward.
Some things that changed in 2015 is Santiago started throwing a slider (thanks Mike Butcher?), and he threw his sinker and screwball almost not at all (though to be fair those were rare pitches for him - he threw 125 of them in 2013 and 39 in 2014). His curveball usage also dropped in 2015 and again in 2016. I'm not sure what prompted Santiago to stop throwing screwballs since he was getting a 10%+ whiff rate on them (close to being higher than his his fastball, cutter or curve).
If you dig deeper into Santiago's numbers, you'll find that he does okay the first time through the batting order, but does give up a fair amount of hits and homeruns early in the game. The second time through is usually his best, and by the 3rd trip through the lineup things don't look so good.
Batting average by pitch category and times through the order (2015-2016):
Slugging PCT by pitch category and times through the order (2015-2016):
Also for some fun - I present to you all 14 of Santiago's homeruns allowed in 2016 - mapped to the strikezone:
April 7 - Cutter
April 12 - Cutter
April12 - Changeup
April 23 - Fastball
April 29 - Fastball
May 4 - Changeup
May 10 - Fastball
May 20 - Sinker
May 20 - Sinker
May 20 - Sinker
May 25 - Slider
May 31 - Sinker
May 31 - Changeup
May 31 - Sinker
No one is buying Santiago's sinker anymore, so it's maybe a good thing he doesn't throw it as much as he used to. Of course, the data is only so accurate since a sinker and his two-seam fastball can be interchangeable in the data depending on movement, and a cutter and slider can sometimes have the same issue. It is interesting that 5 of his last 7 homeruns allowed were either sinkers or possibly two seamers.
And of course, there is pitch placement. You can look at the chart above and see that all his homeruns allowed have been int he zone, and it mostly pretty hittable locations. You throw a sinker or two-seamer right at the top of the zone in the middle and you are looking for trouble. Almost all of his changeups were thrown right in the middle of the zone as well.
The biggest question might be, can Santiago handle the pressure?? He seems to do well in high leverage situations in game (like bases loaded), but he doesn't do well as a game wears on, and perhaps being thrust into the ace role has put more pressure on him than he can handle.
I've always thought Santiago was a perfectionist that is really hard on himself (many pro athletes are). I think the problem between he and someone like Kershaw or Arrieta is they get back on the horse and get back to it. When Santiago starts to boil over, it lasts too long as you saw in his recent ejection. Way more than one time I've seen Santiago show visible frustration throughout a game, which is really not conducive to a good pitching outing. Frustration from a manger? Great! Frustration from a pitcher who needs to focus? Not so great.
Santiago has good stuff. He has good velocity. He may even be ace material some day, but that will never happen until he controls his frustration better, makes smart pitch choices, and stops giving up the long ball (which is partly related to the prior two).