Flaherty has to cut down on the walks, especially to a player like Descalso.
Flaherty’s walk rate is 2.45 per 9, which is just outside the top 30 of starting pitchers this year. Prior to yesterday, he was hovering around the top 10. So it’s not his walks that is the issue. Also, the Descalso “walk” included one pitch in the strike zone and another that was called a strike most of the day (the 3-2 slider). Descalso may have even swung at the fastball that was in the zone.
That said, Flaherty’s real issue is home runs. He has the 5th worst home run rate in the league, and is dead last among starters in HR/fly ball%. He was near the bottom of the boards last year as well. Unfortunately, that may always be an issue as a guy without great stuff who pitches in the zone is likely to get whacked. That limits his ceiling, IMO. The best version of Jack looks like a guy who can eat innings with a low-mid 3s ERA and decent K rates who always gives up too many HRs. In his better years he may dip lower but it’ll probably be on the strength of a “lucky” low BABIP or HR/FB rate rather than anything else. There isn’t anything wrong with having a strong #3/weak #2 guy like him.