South Sydney officials have lodged a complaint to Penrith after Sam Burgess was struck in the face by a spectator as he left the field after the Rabbitohs' 18-2 win over the Panthers on Friday.
A female supporter hit the England international just above the eye with a flagstick as he walked towards the change rooms.
Burgess didn't sustain any injury and declined to comment on the incident.
However, Burgess' mother Julie vented her anger on Twitter.
"Would love to meet the woman (I'm being kind) who hit Sam with a stick as he was leaving the pitch. Sorry Penrith people but that's not OK," she wrote.