His last start at home against Boston his fastball in the first inning was his usual 93-94 MPH. By just the third inning it was down to 87-88 MPH. It seems he isn't able to keep throwing in the mid 90 's as the season goes on. Either he is too weak to keep up his normal pace for a full season, or the weight of all his hair is too much for him.
The other reason for the line, which seems more likely, is that SF is on a 6 game losing streak and the entire team seems in a hitting slump. I played Colorado tonight.