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Madison Bumgarner is discovering his curveball

San Francisco's ace southpaw has had his best professional year to date, and his bender has contributed the most to that.

This powerful hitter has done pretty well at that whole pitching thing too.
This powerful hitter has done pretty well at that whole pitching thing too.
Lance Iversen-USA TODAY Sports

The offensive prowess of Madison Bumgarner has received a lot of attention recently. My colleague Chris Teeter wrote about Bumgarner's batting breakout before he crushed his fifth home run of the season. But Bumgarner's accomplishments at the plate shouldn't obscure what he's done on the mound or the pitch that he's ridden to get there. Unlike in past years, Bumgarner may have some competition for the title of best pitch in his arsenal.

Bumgarner has always been a very good pitcher. Since he joined San Francisco's rotation full-time in 2011, his 19.7 WAR ranks ninth in the majors, while his 17.9 RA9-WAR places him 15th. However, he's done better than ever before in 2015:

Year RA9-WAR Rank (Percentile) WAR Rank (Percentile)
2011 3.2 38th (60th) 4.9 10th (89th)
2012 3.1 37th (58th) 3.1 28th (68th)
2013 4.2 20th (75th) 3.8 22nd (73rd)
2014 3.4 30th (66th) 3.9 18th (80th)
2015 3.8 17th (81st) 4.0 12th (86th)

His WAR has progressed steadily since 2012, and his RA9-WAR has jumped up after bouncing around for a while. Bumgarner has done something differently in 2015 to take the next step.

The cutter has long excelled for Bumgarner. Only three other pitchers* can best its 63.9 runs above average over the past five years. Like Clayton Kershaw's slider or Felix Hernandez's changeup, it's one of the true dominant pitches. Last year in the playoffs, though, another of Bumgarner's offerings grabbed the headlines: the curveball. After making hitters look dumb in the NLCS against the Cardinalsit dominated throughout the World Series, helping him earn his third ring.

*FanGraphs calls it a slider.

Perhaps Bumgarner learned from that success, because he's relied on the curveball more than ever in 2015:

BumCurve

In its place, the cutter's usage has decreased. This trend becomes even more pronounced when Bumgarner gets to two strikes:

Two Strikes Cutter Curve
2011 39.8% 13.4%
2012 47.5% 11.8%
2013 37.9% 20.7%
2014 34.3% 18.5%
2015 21.8% 29.5%

The curveball has become Bumgarner's out pitch, replacing the cutter. Based on what Bumgarner's achieved thus far — he's on pace for his first-ever five-win season in both WARs — I'd deem this a worthwhile change.

Why would Bumgarner alter himself in the first place? The cutter had succeeded in the past, so messing with that could have put him at risk of falling behind. He would have shifted his approach only if he knew that the curveball could handle the heat. By several metrics, the pitch has always topped the cutter.

Swinging strikes generally tell us a lot about a pitch's efficacy. They indicate a level of dominance that no other outcome can match. Thus, the fact that hitters have whiffed at 15.2 percent of Bumgarner's curveballs since 2011, compared to 12.7 percent of his cutters, soundly endorses the former. Those pitches' respective 2015 marks of 18.3 and 14.9 percent mirror that disparity and have a lot to do with his career-high 26.5 percent strikeout rate.

In terms of batted balls, the cutter has generally beaten the curveball, whose 51.7 percent ground ball rate and 3.4 percent pop-up rate over the past five seasons don't compare favorably to the cutter's 52.6 percent and 6.2 percent. With that said, 2015 has seen the curve improve significantly in both regards, its grounder clip increasing to 56.1 percent and its pop-up rate spiking to 6.1 percent. Not only has the opposition made very little contact against the pitch, but they haven't capitalized when they've put it in play.

This change doesn't come without danger. Curveballs, at least in theory, can carry a greater chance of injury to pitchers who throw them heavily. Nevertheless, Bumgarner hasn't dealt with any notable ailments in the major leagues, a characteristic which tends to predict future injury. Plus, cutters don't have a sterling reputation with regard to keeping their owners healthy. Along with the better results on the pitch, this justifies Bumgarner's decision.

As the Giants trade blows with the Dodgers for first place in the NL West, they'll need Bumgarner to maintain his current hot streak, both hitting and pitching. If no malady befalls him, he'll likely ride his curveball to continued superiority. The cutter-heavy Bumgarner of old has disappeared, and a better version has replaced him.

. . .

Brooks Baseball data does not include Friday's game.

Ryan Romano is an editor for Beyond the Box Score. He also writes about the Orioles on Camden Depot (and on Camden Chat that one time), and about the Brewers on BP Milwaukee.