Trap Runner

Text:

: Target unblocked attacking creature becomes blocked. Activate only during combat after blockers are declared. (This ability works on creatures that can't be blocked.)

Rulings:

• 10/4/2004 If the ability is used on a creature with Trample, the damage still comes through.
• 10/4/2004 This ability will trigger any creature’s “whenever this becomes blocked” ability.
• 9/20/2013 If a turn has multiple combat phases, the ability can be activated during any of them as long as it’s after the beginning of that phase’s Declare Blockers Step.