[theflyinghorse]

Controlled, ability based violence! Aka martial arts with an emphasis on live training.

I do jest only somewhat. As a personal anecdote I find sparing to be a tremendously positive tool to get my mind off of work and daily troubles.

[adrianN]

Whether taking punches is healthier than weed or alcohol is of course questionable.

[theflyinghorse]

Depending on the particular martial art strikes could be light or even missing entirely as is the case of grappling arts such as judo or jiu-jitsu thus lessening the risk of head trauma.

[achenet]

Agree that judo/jiu-jitsu have far less risk of head trauma/concussion, but as far as sports go they are still relatively dangerous - I quit after having one too many injuries.

I would say probably the safest sport, and my current favorite, is Olympic weightlifting, although climbing is in many ways similar to jiu-jitsu, and much safer.