Australian rules football, with no padding, and less rules would be my guess.
I was thinking of a cage match where the observing mechwarriors kept handing chairs in through the fence's openings.
(http://prommanow.com/wp-content/uploads/2015/12/ambrose-sheamus-steel-cage.png)
But . . . Hellraiser is right, Trials of Possession and Grievance as part of the touman are guided by some unofficial rules depending on the situation and Clan. I want to say there was a freebirth Star Colonel among the Warden Wolves who had fought something like 20 trials about his position with most of them at the end coming from outside his unit, the insinuation was that it had to do with his being a freebirth. He was so popular in his own cluster as a commander that his subordinates took a dim view of anyone challenging.
As a individual warrior you also had to weight the risk of pissing off the commanding officer of the officer you were challenging. I want to say we get a few conversations where a Galaxy Commander or Star Colonel let a Star Captain or Star Commander (respectively) know they would be very unhappy if the lower ranking officer challenged his superior- and implied he might not survive his superior's displeasure.
IMO, this comes down to RP/character development . . . folks tend to just throw out- well challenge for the position. But to challenge you must have a case or it can turn things against you- superior officers who view it as a distraction & waste of time and the challenger's peers who may not approve.
Consider Conner Rood . . . he did not challenge Montrose during Operation Icestorm even though he knew the situation was falling apart and that it could end his Clan. He was considering the implications and results of what would happen if he challenged during the midst of the campaign. Should he have challenged her after the attack on Wotan? Well, the Hellions hit the Falcon OZ with four or five galaxies (Alpha, Beta, Delta, Zeta and Zeta Prime?) along with a handful of warships escorting their JS . . . and left in a Potemkin with a pair of clusters & keshik. The situation was that bad, and yet he did not challenge because in his opinion it would break the Clan's unity.