Ke'Bryan Hayes is an extremely frustrating player. Last year, he only batted .244/.341/.345 through 560 plate appearances. He had an above-average 8.6% walk rate and a 21.8% strikeout rate. He was also in the 75th percentile of whiff rate and 63rd percentile of chase rate, so he has a good eye at the plate. However, despite having a 91 MPH exit velocity (top 85th percentile) and 46.8% hard-hit rate (top 84th percentile), Hayes hits for almost no power. He was barely in the triple-digits of ISO at .101 and overall had just a .294 wOBA and 88 wRC+.
Where Hayes struggled was lifting the baseball. Hayes had a launch angle of just 5.2 degrees. Hayes does have an exit velocity in the 85th percentile and a hard hit rate in the 84th percentile; Hayes' barrel rate was just 3.9% and in the bottom 13th percentile. This is what makes him such a frustrating player to watch. No player in the Statcast era has ever posted such good remarks in both exit velocity and hard-hit rate and has fallen shy of the 20-home run plateau in 500+ plate appearances until Hayes this year.
While Hayes needs to make this adjustment, he's not too far off from being a good hitter. He doesn't need to pull a Joey Gallo and focus all his effort into a launch angle of nearly 25 degrees. Guys like Alejandro Kirk, both Willson and William Contreras, Juan Soto, Nate Lowe, Bo Bichette, and Jose Abreu all had comparable exit velocity and/or hard hit rates, yet all had a sub-10 degree launch angle.
If Hayes figures this one thing out, he will be one of baseball's most valuable players. Everyone knows, or at least should know, how great of a defensive third baseman Hayes is. He had +24 defensive runs saved, the most by any player last year, along with +18 outs above average, the third most in the sport. On top of that, he had a quality +7.2 UZR/150. He's even a good base runner, swiping 20 bags in 25 attempts.
Give Hayes an 8-degree launch angle, and wait for the 5.0+ fWAR season. Hayes is so close to becoming such a complete player, with power, plate discipline, fielding, and base running. All he needs is this one adjustment, and you'll start seeing a ton of offensive production from the third baseman.