My dad did a similar thing one time.  He was in the process of teaching my young cousin to water ski, she was intimidated by the boat, so he had her in shallow water, holding on to the rope, facing shore, maybe 50 feet out.  
He was on shore, and would run with the rope, so she could get the "feel" of the skis when you are starting to be pulled through the water.  (She was only 6 or so, so he was able to run fast enough that she could almost stand up as he was pulling her)  
One pull, he was sprinting at full speed, looking back at her, and ran SMACK into a tree head first.  He just laid on the ground for 15 minutes, then ended up going to the doctor because his knee swelled up the size of a grapefruit.  Good times, good times.