In-season training may be the most confusing and misunderstood component of the year long training cycle.  Everybody knows that it is important and must be done but getting better at your particular sport should be the main goal during the season.

That being said, I think in-season training might be one of the most important time of the year to train.  Sure the off-season and pre-season are important, but the goal should be to be at your physical peak for the END of the regular season and post-season tournaments. 

To attain that peak means that the correct steps must be laid down prior to the conclusion of the season. My philosophy of in-season training might be quite different than others but I believe it to be extremely simple and easy to implement.

DO THE OPPOSITE OF THE SPORT

Huh?  What does that mean? Shouldn't we be doing things specific to make them better at their sport?
I strongly disagree that we should be doing the similar patterns on the sport - this can lead to overuse type injuries that we are trying to prevent against.  We want to keep the athletes as healthy as possible so they can be at their physical peak for the end of the season.
Most team sports have the following similarities in-season:
1. High Volume of Activity
2. Low Loads being used - typically just their bodyweight
3. Low Amplitude of movement - never experience full joint range of motion during most sporting activities.

 So according to my statement above of DO THE OPPOSITE OF THE SPORT we have the following guidelines of in-season training:

1. Low volume of in-season strength training
2. High Loads to stimulate higher threshold motor unit activation for strength maintenance and/or gains
3. High amplitude of movements to restore and enhance joint mobility.

These guidelines help me direct how I write training programs and progress them throughout the season so we are ready to peak near the end of the year. Other common sense guidelines that can be used are the following:

1. If your sport is inherently anaerobic, train the aerobic system for extra conditioning
2. If your sport involves a lot of impact (running, jumping) - don't run and jump them extra.
3. If your sport has a dominance of the anterior chain, train the posterior chain to balance things out.
4. If your sport has a tendency towards kyphotic postures, hammer thoracic spine extension.
5. If your sport has a tendency to lose mobility in a certain area (i.e. ankles, hips), address those issues.
6. If your sports practice structure doesn't include much conditioning, then this must be included to conditioning levels do not decrease in-season.

By now, I think you can get the point of how in-season training can be accomplished. These are extremely general guidelines but simple and tends to make a lot of sense. Hopefully they can help you and feel free to share what your thoughts are.