Originally posted on Fangraphs  |  Last updated 7/26/12

Aroldis Chapman is hot. His fastball tops 100 mph. His slider is nearly unhittable. And he’s on the verge of breaking two strikeout records.

In 47.2 innings pitched through Wednesday, the Reds closer has racked up 16.99 strikeouts per nine innings, the highest in the majors this season for pitchers with at least 30 innings under their belt. In July, in 11.1 innings pitched, his strikeouts per nine innings has jumped to 20.65.

But it’s not just the number of strikeouts he’s recorded. It’s the lethal efficiency with which he’s dispensed with his adversaries. Chapman has struck out nearly half the batters he’s faced this season, posting a 49.7 strikeout rate through Wednesday. He’s faced 181 batters. He’s struck out 90 of them. In July alone, Chapman’s strikeout rate is at 65%. Forty batters faced. Twenty-six strikeouts. Oh, and he has a negative FIP for July.

Look at those numbers again and let them sink in. Almost unfathomable.

Since 2002 — the first season for which monthly splits are available — only one qualified reliever recorded a monthly K/9 higher than Chapman’s current 20.65 K/9 in July. Dodgers closer Kenley Jansen had a 21.07 K/9 in September, 2011.

Other than Jansen, only three qualified relievers have posted a K/9 of 18.00 or higher in any month from April 2002 to the present: Rafael Betancourt in August, 2010; Takashi Saito in June, 2008; and Darren Dreifort, in June, 2004. Since 2002, no qualified reliever has posted a monthly strikeout rate of 65%. The highest is Jansen’s 61.5% in September, 2011.

If Chapman maintains his season-long pace, he will establish new records for K/9 and K% for qualified pitchers dating back to 1918. The K/9 record was set just last year by Jansen. In 53.2 innings pitched, Jansen recorded 16.10 strikeouts per nine innings. This season Chapman is striking out almost one additional batter per nine innings. The K rate record is held by Eric Gagne, who struck out 44.8% of batters he faced in 2003, the year he won the National League Cy Young Award. Chapman’s currently at 49.7%. To be fair, Craig Kimbrel of the Braves is also ahead of Gagne’s 2003 pace so far this season. His K rate is at 45.8% in 39 innings pitched through Wednesday.

The key to Chapman’s strikeout madness is a fastball that averages 97.8 mph but runs as high as 102.4 mph and a slider that averages 88 mph and tops out at 91.7. He also throws a changeup, but rarely. Indeed, about 80% of Chapman’s pitches are fastballs. With that kind of velocity, his pitch mix isn’t terribly surprising.

And what happens when Chapman throws his fastball? Batters know it’s coming and, for the most part, they still can’t do much about it. It looks like this:

Chapman’s swinging strike rate on his fastball is 18.7%, the highest in the majors so far this season. Glen Perkins of the Twins is next, with a 17.4% swinging strike rate on his fastball. Joel Peralta of the Rays follows Perkins, at 16.9%.

For a secondary pitch, Chapman’s slider is nasty and effective. It looks like this.

The swinging strike rate on his slider is 22.3%. That doesn’t lead the majors but it’s pretty close. Boone Logan of the Yankees has posted a 23.9% swinging strike rate on his slider so far this season. Sergio Romo of the Giants is at 23.7% on his slider. But neither Logan nor Romo has a fastball anywhere near as effective as Chapman.

Aroldis Chapman is dominating batters and making them look silly. His strikeout numbers in July are off the charts. So too are his season-long numbers so far. If he keeps up this pace, he will shatter the record for highest K/9 and strikeout rate in a season. It’s amazing, and it’s very fun to watch.

Many thanks to Carson Cistulli for creating the .gifs for this post.

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