Lions are pretty strong but Jaguars are much stronger than any lion or lions and would overpower a lion easily.
If a Jaguar and Lion were to get into a fight the Jaguar would win the fight.
That is unless there were more than one lion that were to come up against the one Jaguar.
If there were more lions in the fight than Jaguars then the several lions could more easily overpower and kill the Jaguar.
But if it was just the Jaguar and one Lion then the lion would likely be the one killed because Jaguars also have a much stronger bite than a lion.
However if a regular Tiger and a Lion came up together in a fight then the Tiger would overpower the Lion because the Tiger is much more powerful than the Lion.