The pitch was 99 mph. On the inside corner. Ian Stewart watched helplessly as it zipped past his knees and into Ryan Hanigan's mitt for the called third strike. Inning over. Bases-loaded threat stifled. The pitch, which came in the seventh inning of Sunday's 4-3 Reds victory over the Chicago Cubs, evoked some "un" words – unhittable, unfair, unbelievable.

The pitch illustrated perfectly why Aroldis Chapman has been arguably the most dominant pitcher in baseball so far this season: When he can throw it where he wants it, the hitter has virtually no chance.

Chapman, a 24-year-old Cuban left-hander, has thrown 10 1/3 innings this year. He's allowed three hits and no runs. He's walked two and struck out 18.

Chapman, of course, is the same guy who walked 12 batters and gave up 10 runs over a four-game, 1 1/3-inning span last May.

How did he get so much better?

The answer: Lots of reasons.