BOSTON — The Astros announced Friday that center fielder Justin Maxwell, who fractured his left hand on Tuesday after being hit by a pitch, is estimated to return to competition in 4-6 weeks. Lefthanded pitcher Rudy Owens, who’s on the club’s 40-man roster and assigned to Class AAA Oklahoma City, has a stress fracture in his left foot that will require surgery. Maxwell, 29, fractured the fifth metacarpal of his left hand but doesn’t require surgery. The fifth-year veteran is wearing a splint. Maxwell hit .234 with one home run and six RBI in 20 games for the Astros, starting the first 20 contests of the year in center field. [...]