What is the most dangerous predator that a human could beat realistically?

No weapons, tools etc allowed. Flat terrain, fight to the death. The human must have a good chance of winning.

Scenario 1: The human is average, 175 cm tall, male, normal strength, etc.

Scenario 2: Peak human. The human must exist, so pick the strongest person you can think of.

Edit: All time periods are allowed, so dinosours are an option. land animals