Board Thread:Legitimate Canon Questions/@comment-26896410-20150816144824/@comment-4091815-20150816190138

The nogitsune was already inside Stiles at the time of the William Barrow confrontation during Galvanize.

Stiles was hit with Kira's electricity (foxfire). It was enough to magnetize his metal baseball bat and boosted a somewhat weakened Notgisune spirit that was already inside Stiles.

Derek speculated that this jolt of electricity (foxfire) was what the Nogitsune was after and the only reason it had Barrow go after Kira.