Speaking from my experience of playing SS most of my life, players who are normally accurate, but throw wild under pressure situations, are showing signs of mental weakness, not physical. Plouffe needs to just relax, breathe, and not panic. It's a mental thing that can be fixed to some degree. Perhaps not fixed completely, but at least limited or reduced. He needs to to be consciously aware of what's going on in his mind in these situations. He needs to be mentally prepared for these situations every pitch the same way he has to know in his mind what he's going to do with the ball each play if it's hit to him. It's difficult to explain, but it's almost like your fight or flight response kicks in (spiked heart rate) and your body just doesn't respond the way it normally does. It's a result of being human.