Well it depends on the terrain and where they start and technicalities. If they were far apart, Hawkeye could just shoot cap with all different types of arrows and destroy him. If it were close combat, then Hawkeye is about to die
well hawkeye can shoot multiple arrows per second and so all he haz to do is shoot an arrow of explosives around cap and blow him up lel
Let's not forget that Cap has withstood 60 years in ice (he's tough) and he has a shield made of the strongest element (it reflected a laser blast from Iron Man and a hammer blow from Thor's hammar).
Ik. But if they were far away Hawkeye can just spam explosive arrows at Cap. If it were hand to hand Cap would rekt I agree on that.