Ok, I know this is wrong to do, but....
Football: Short bursts of extreme energy. Can take a toll on body do to impact injuries.
Basketball: Constant movement with sporadic bursts of energy, sometimes extreme. Injuries can occur do to jumping and planting of feet and legs. Not much contact.
Baseball: Little movement, except for sporadic bursts of energy. Frequency depends upon position. Right fielder to pitcher is order from least energy to most that will likely be expended by a player. Injury to ball strikes in at bat situations is possible, and although may be severe, is not regularly occuring.
Soccer: Constant running movement, in all cases except for goalie. Goalie may have extreme bursts of energy, or quick constant movement for brief periods of time. Forwards/sweepers will expend most amount of energy as the travel the farthest distances up and down the field of play. Injuries common to running and jumping common. Also accidental and sometimes intentional collisions between players may happen. (Soccer can be more dangerous to the fans!)
Hockey: Constant movement for all players except goalie. Extreme bursts of energy expended regularly. Injuries from impacts often occur. Player to player body hits. Stick to player hits. Player to player and wall hits. Puck to player hits. Players fighting.
I've played every sport I just listed except hockey. I'd say football has the most regular risk of getting injured seriously, while hockey leads to more injuries overall.
In order of endurence (High to low):
Basketball
Hockey
Soccer
Football
Baseball
In order of injury risk (high to low):
Football
Hockey
Soccer
Basketball
Baseball