Several hours before the start of Sunday’s game between the A’s and Houston Astros, as a handful of A’s hitters took batting practice at the Coliseum and pitchers stretched and played catch down the left-field line, a slender, solitary figure in a green warmup top leaned against a section of fencing near the A’s dugout, watching. Jesse Chavez hurls a pitch during Sunday’s game against the Astros, in which the right-hander earned his first major-league victory as a starter.