Hammel's slider helping fuel great season

Last July's huge trade between the Cubs and A's is often remembered as "Jeff Samardzija for Addison Russell," but that tends to leave out a player who has ended up being pretty important on the North Side. (Not you, Billy McKinney. Yet, anyway.) Jason Hammel, who also went with Samardzija to Oakland, has proven to have been very useful to the Cubs in a few different ways.

At first, it was simply turning a mere $6 million one-year investment by Chicago into 108 2/3 innings of very good work, leaving Chicago with a 2.98 ERA. Then, it was helping to bring back the top prospect Russell, because he was so highly regarded that it took the Cubs two good starting pitchers to get him. Now, having returned to Wrigley Field on a two-year contract this past winter, all Hammel has done is pitch like one of the best pitchers in baseball, ranking eighth in the Majors in Wins Above Replacement.

Hammel is not quite that good, of course. You shouldn't ever judge present-day talent by the current partial season alone, not when there's so much more data in the past to incorporate, but after a career-high 11 strikeouts in Chicago's 5-1 win over the Marlins in Miami on Monday night, it's hard to not be impressed by what he's done, and how he's done it.

For the second consecutive year, Hammel has increased his strikeout percentage, going from 15.7 percent in 2013 to 22.1 percent to 26.3 percent. For the fourth consecutive year, Hammel has decreased his walk percentage, going from 9.2 percent to 8.5 percent to 7.0 percent to 6.2 percent to 2.7 percent. That's another way of saying that in 67 innings, he has a 69/7 K/BB ratio, and since three of those walks came in one game, he's walked one or fewer in nine of his 10 starts. The ensuing 9.86 K/BB ratio is the third best in baseball; Hammel's K percent-BB percent is the sixth best, behind some heavy names like Scherzer, Kluber, and Kershaw. Hammel's 65.7 percent first-pitch strike percentage is easily the best of his career.

So what's changed from the Hammel who was regularly having trouble missing bats and keeping runs off the board for the majority of his career? Well, getting out of Coors Field, where he pitched between 2009-11, certainly didn't hurt. It's also because Hammel has stopped relying so heavily on his good-but-not-great four-seam fastball, which had been his primary pitch as a Rockie, and instead began to lean more on what's become a very good slider.

Percentage of slider use -- wRC+ against
2013: 20.99 percent -- 118
2014: 31.77 percent -- 49
2015: 35.96 percent -- 16

wRC+ is "Weighted Runs Created Plus," which is set to an average of 100, so Hammel's 2013 mark can be read as "hitters were 18 percent better than average" against the pitch, and that 16 figure means hitters are 84 percent worse than average this season. The more he throws it, the better it's been, in part because he's gained separation on it from his fastball -- it's slowed down about two mph in the past two years as the fastball has remained steady -- and gained more than an additional inch of vertical movement on it. 

With Statcast™, we can see another reason why the slider may be so successful. On both of Hammel's fastballs, he gets similar pitch extension of 6.46 feet (four-seam) and 6.53 feet (two-seam). With the slider, that's 5.76 feet, and while that might not seem like much, its seems that hitters aren't picking up on the difference. The perceived velocity on his fastballs seem slightly faster to the eye of the hitter; for the slider, it's a half-mph slower.

Now, up above, we said that Hammel couldn't be expected to pitch like this all year long, and part of that is self-explanatory, simply because it's pretty rare for 32-year-old mid-rotation starter to suddenly turn into an ace. But we might also see clues in the Statcast™ data, because Hammel got hit harder in May than he did in April (average exit velocity up from 84.69 mph to 88.97 mph), and in Monday's game, he gave up a few screamers. Five balls came off the bat at 92 mph or higher, and two topped 100. Giancarlo Stanton's fourth-inning single at 114.78 mph was actually one of the 14 hardest-hit non-homer balls tracked all season. It won't matter if they're not making contact, but the contact is getting louder.

Even so, Hammel doesn't have to be this good to be valuable to the Cubs. After all, he's done more than his part for the franchise already.