Their bodies.
Kids on my son's H.S. team are all seeing injuries pop up. Last year many went from H.S. baseball, to travel summer, to travel fall and then a wood bat league.
2 months off and now right back at it.
My son took H.S. off because of an injury. Played a little summer travel. No fall or wood bat and just focused on training. He is not seeing any of the other injuries and his coaches have all said he looks way more fresh than the others.