Who would win a polar bear or a piranha?

the bear they are a lot stronger
That depends on what type of bear it is. A black bear would lose, but grizzly's stand more of a chance. However, it is possible for a lion to beat a grizzly. When lions fight, their target is the throat and legs. Breaking the air pipe would suffocate the bear, and damaging It's legs would leave it on the ground, where the lion would kill it. But if the lion attempted that, the bear may kill the lion first.
A kodiak bear, grizzly bear, or polar bear could kill a lion, but a lion could kill a black bear.

Another AnswerA lion can kill any type of bear because a lion has powerful biting force and great fighting skills.