Can a thief backstab the player he his helping in combat

[larsp360]

Another thief question, can the thief (who was sucked into combat via dwarf toss) discard his equipped and active weapon/armor/bonuses to backstab his "partner" in combat in an attempt to get them to run away/die?

Moderator edit: Since this question is not a follow-up question to a response to the original question in the thread in which it was posted, it was moved it to its own thread. We moderators prefer that new questions get their own threads to improve the chances of future searches finding the answers.