Not quite sure what you mean; what card(s) would you give if one player was holding an opponent while another punched him?
Typically players are held by other players from their own team.
A "handbag" punch on an opponent which might see Yellow normally could change into Red if there is a team-mate holding him, but in my limited experience of rugby union brawls, there are worse things to worry about.
But since you are asking what I meant: an offence under law 10 in the normal course of play tends to be blamed on a single individual (as opposed to a brawl where there may be multiple cards for multiple offences, or simply for the sake of equality).
In summary: a physical attack on an opponent who is able to react might (might!) be a Yellow, but escalation to Red for defenceless players attacked whether they be stuck on the ground or held/bound by others. I would not card the ground for being below a player being stamped on.
