The number of reps is described as follows:

• “10 reps alternating” means you do 10 total reps, alternating right and left sides. So you’ll wind up doing 5 reps on each side.
• “10 reps each side” means you do 10 on the left continuously, then 10 on the right.
• FOB means “feet on the ball” while HOB means “hands on the ball”