https://blogs.fangraphs.com/four-hitters-who-should-have-your-early-season-attention/
Chapman headlines the article, he has changed to a toe-tap timing mechanism. Seems to be paying off.
"The difference in Chapman’s connection to the ground is drastic. Last year, he hit full front knee extension and immediately flew off the ground as he over-rotated to the pull side (watch his lead foot come disconnected). This year, his toe tap is allowing his stride to stay closed through foot strike and his feet to stay connected to the ground even after full knee extension, suggesting an improvement in rotational direction. If this is what a toe tap does for him, then I’m excited about his potential going forward."