Whenever Redcap Raiders attacks, you may tap an untapped non-Human creature you control. If you do, Redcap Raiders gets +1/+1 and gains trample until end of turn.
While resolving the ability of Redcap Raiders, you can’t tap more than one creature to get +1/+1 more than once.
Tapping an attacking creature with vigilance to pay the cost of Redcap Raiders’s ability won’t cause that creature to leave combat or to stop attacking.
Players can’t take any actions between the time you choose whether to tap a creature and the time Redcap Raiders gets +1/+1 and gains trample.