What's the strongest animal a fully armored knight with a longsword could beat 50% of the time ?

Our knight in this scenario is a 5'8 169lb dude that is extremely athletic, and he's been training for several years, he has no diseases that would negatively affect him and he's extremely skilled at using a longsword The battle takes place in a temperate forest were both the animal and the man are willing to fight to the death, now that the location is set what's the strongest animal he could beat at least 50% of the time