The goals of any in-season program are nearly identical: Maintain strength and power (upperclassmen) or improve strength and power developed in off-season programs (freshman and redshirts).
The only difference between in-season training for football and in-season training in any other sport is that football coaches and football strength coaches place a greater emphasis on in-season strength training. Other sports would benefit from doing the same.
In sports such as soccer, consistent training during the in-season period will form the backbone of the long-term success of the strength program and the sport program. Bottom line: It's much easier to get stronger in the off-season when you maintain strength during the season. It's a waste to spend off-season time regaining lost strength.
In high school or college sports, look at your training program as a four-year process. In an ideal world, progress will be an upward progression of strength, power, and speed every year.
1. Train Frequently
Realistically, you should train two workouts per week with higher intensities but lower volumes. Intensity is the key to training, not volume, and this applies even more during the season. Never skip an in-season workout. A 15-minute, one-set workout is better in the long run than a missed day of training.
2. Work Lower-body Strength and Power In-Season
Don't "save the legs." If you save them in September, they will fail you in November. See number one above. High intensity, low volume. One or two sets of an Olympic lift and one or two sets of a squat or variation go a long way.
3. No Excuses
Only listen to "workers," not "whiners." Athletes hate in-season lifting. It's like going to the dentist. Painful, but necessary.
4. No Optional Workouts
Don't make excuses with "choices" of lifts, or phantom injuries that get you out of working your lower body. We need to convince sport coaches that if athletes are too injured to lift, they are too injured to play. You'll be amazed how fast kids get healthy.