Complex sentence: In, Kingman's enigmatic personality (which former Mets teammate John Stearns once compared to a tree trunk) began to assert itself, as he dumped ice water on a reporter's head during Spring training.
Split into simpler sentences: In, Kingman (whose personality former Mets teammate John Stearns had once compared to a tree trunk) began to assert himself more outwardly. He dumped ice water on a reporter's head during Spring training.