<p>Definitely a tie between conditioning and injury, as well as warm-ups/stretching, or lack of, and injury. Almost all the injuries that my sons sustained in sports resulted from a lack of proper stretching beforehand (hamstring/ankle injuries during sprints or long jumping), or after-game care (such as icing down a pitching arm), or insufficient conditioning (too many pitches early in the season). There is a tendency for young folks to not take stretching beforehand seriously. There is a tendency for young players in certain sports not known for danger (like baseball or track) to not take conditioning seriously. Maybe that is why football does not have the high rates of injury one would suspect. Because it is considered dangerous, coaches go to extremes with warming up, exercising, conditioning, weight-training, pushups, windsprints, etc. MONTHS before the season even begins.</p>