There was a time when it was indisputable that Craig Kimbrel was the best relief pitcher in baseball.

During his rookie season in 2011, he went 38.1 innings without giving up a run. In 2012, he became the first pitcher in baseball history to strikeout at least half of all batters faced and had an ERA of 1.01. In 2013, he became 1 of 11 pitchers in MLB history to save 50 games in a season. He also became the fastest pitcher ever to reach 400 career strikeouts, doing it in 236 innings, which took place during the 2014 season.

In 2015, Kimbrel was traded from the Atlanta Braves to the San Diego Padres, where he became the fastest pitcher to reach 200 saves. He was then traded to the Boston Red Sox the following offseason, where things took a sharp turn downhill.

He hurt himself at the start of last season with a knee injury, and then proceeded to post subpar numbers (for him) across the board. His 3.40 ERA and 5.09 walks per nine innings were both career highs, and his 31 saves were a career low.

But now, in his second season with Boston, Kimbrel is pitching better than he ever has before.

In 17 games (17.2 innings), Kimbrel has an ERA of 1.02 and a fielding independent pitching (FIP) of 0.42. He is striking out an insane 17.32 batters per nine innings, which is tops among relief pitchers. He has a whiff rate of 54.8%, which is also the best in MLB. He is averaging nearly two strikeouts per inning, and perhaps even more shocking, he has walked just two batters all season.

Earlier this month, he threw an immaculate inning against the Milwaukee Brewers, striking out the side on nine pitches. He was only the 78th pitcher in MLB history to do so at the time.

He has retired 43 of the last 46 batters he's faced, and 23 of the last 24. Opponents are hitting only .102 against him, and right-handers have yet to record a hit off Kimbrel this season. Based on the video below, it's easy to see why.

Kimbrel's fastball is averaging 97.9 mph this year, up slightly from 2015-16 when he averaged 97.3 mph, and hitters are swinging through it at a greater rate than ever before. In 2017, 44.8% of swings against his fastball have resulted in misses. Last year, that number was 28.0%, and even in 2012, at the height of his powers with Atlanta, it was only 38.6%.

The big key seems to be the movement on Kimbrel's fastball. This chart by Brooks Baseball shows more horizontal movement towards right-handed hitters than at any time in his career.

At this point, there may only be one way to stop Kimbrel's rampage against the American League. Import Philadelphia Phillies fans to sit behind home plate to distract him.

At this point, it's really the only option for Kimbrel's opponents.