This has led to escalating measures to defend the statues from every knavish indignity each school's fans could conjure.
Tommy Trojan, which is usually wrapped in duct tape for protection, has been defended for years by the so-called Trojan Knights. But that hasn't protected Tommy from being doused with blue paint or having its sword cut off and reattached in, well, not the right place.
At UCLA, students began aggressively patrolling overnight after their bear was doused in red and yellow paint five years ago.
In recent years, the bear statue has been tucked away in a "puzzle box" as the big football game draws near, just to be safe.
But on Thursday morning, a group of vandals found a chink in UCLA's armor: timing.
They got to the bear well before anyone thought it was necessary to protect it.
The group sprayed "SC RUNS LA" in red across the bear's torso, a full nine days before the cross-town rivals are set to square off at the Rose Bowl. Authorities believe the pranksters struck several hours before the
UCLA officials and Bruin fans were caught by surprise.
"Crazy Trojans are looking ahead," tweeted @GoJoeBruinUCLA.
"The private university across town had a game against a different opponent last night," UCLA spokesman Phil Hampton said, explaining why the move was unexpected.
Hampton said the incident is believed to have occurred sometime between 2 a.m. and 7 a.m. Thursday. Facilities crews had the statue clean by around 10 a.m., and shortly thereafter the bear was "hibernated" in a dark brown plywood box, he said.
Hampton could not estimate the cost of the cleanup, but said university police were investigating the incident as vandalism. A statue of the late basketball coach John Wooden also was boxed yesterday as a precaution, and fountains on campus (which have been known to turn red at this time of year) will be turned off Friday, he said. The boxes will remain over the statues until after the football game is played Nov. 22.
USC's "Tommy Cam" showed the life-sized bronze statue wrapped entirely in a blanket of silver tape Friday afternoon.
"It's not unusual for there to be different forms of high jinks and vandalism, which is a common but unfortunate manifestation of passion and loyalty in this cross-town rivalry," Hampton said. "Sportsmanship is just as important off the field as it is on the field."
In 2009 someone cut through a tarp and splashed cardinal and gold paint — USC colors — on the bear. The prank was investigated as felony vandalism and it cost $20,000 to restore the statue. UCLA spent another $5,000 for a more secure box cut like a jigsaw puzzle that was placed around the bear. The university doled out another $15,000 for three security cameras around the statue.
As for who tagged the bear this time?
"You can draw your own conclusions," Hampton said.
No word on whether moats are in the statues' futures.