One theory is that football players have crooked legs because they frequently play on uneven surfaces, such as grass or turf. Over time, this can lead to the muscles and tendons in the legs becoming misshapen and causing the legs to appear crooked. Another theory is that football players may be more likely to have pre-existing conditions that can cause the legs to look crooked, such as bowlegs or knock-knees. It is also known that football players kick the ball with their feet turned out, which could contribute to the appearance of crooked legs.