This man encountered the Trickster in his own domain. In the woods this spirit isn't acting out of simple mischievousness. In the woods he has something to protect and any human that gets too close won't be allowed to leave. At least not as a human.

With everything but his underwear shredded the man's body grew a thick coat of fur. His mind started becoming confused. he wasn't sure if he wanted to keep the underwear or not.