I mean obviously some players are simply bad or struggling for reasons completely seperate from coaching/team. But in the specific case of Sheahan it's hard not to see the clear line of declining play since Blashill took over and the clear line of improved play/production since moving to a different team. Sheahan and Dekeyser imo are the most regressed players under Blashill. I hesitate to blame Blashill as much as I just think Babcock knows how to push players buttons. Tatar improved greatly as soon as Babcock got his hands on him. Nyquist suddenly became a big time goalscorer (and since stopped scoring goals under Blash).