Marlins pitchers perform this shoulder stretch twice a day—once in the morning before activity then once later in the day on their own.
Lie on your throwing side with your scapula against the floor. Move your arm in a 90-degree abducted position so your hand points directly at the ceiling. Use your non-throwing hand to internally force your throwing hand down towards the ground. Hold this stretch for about 20 to 30 seconds. Repeat for 3 to 4 repetitions.
"By leaning on the scapula and not falling back, you will be able to work the posterior cuff and help the flexibility of that as well."