From the limited description, the kid doesn't sound like a skinny bastard, so I don't believe this would be the best bet.
How old is he?
How tall is he?
How fat is he? (I don't care about bodyfat %, just round'about - chubby, surprisingly lean/muscular, something else?)
Does he have any experience lifting? Any chance you know his current strength levels?
I'd recommend my go-to bodyweight plan for a bit:
Mon., Wed., and Fri.
Squat 2x15 (No weight, keep both feet flat on the floor.)
Push-up 2x15 (On your toes, go until the chest almost touches the floor.)
Lunge 2x15 (Alternate legs, 1 rep left/1 rep right.)
Neutral-grip pull-up 2x15 (assisted if necessary. Could be substituted with inverted rows.)
Plank 2x15-count (Hold the top part of a push-up, on the toes, arms straight, keep the whole body straight. Count to 15.)
Burpee/squat thrust 2x15
The off-season would actually be a great time to do this, as it would serve as basically a "deload" if he's been lifting already. It will also double as a general assessment.
After that (once the whole workout is easy), it depends on the exact goals, but something simple like Starting Strength or, more appropriately, the original "The Strongest Shall Survive" program (that book's subtitle is, after all, "Strength Training for Football") would be worth considering.
Eric Cressey and Dan John also have some good info about training younger athletes. Just remember to define the goals. What exactly does he need to accomplish in the offseason? Prioritize: Strength, fat loss, speed, rehab, conditioning?