3 And oftentimes he would relent his pace,
oftentimes > many times, frequently relent > slacken
4 That him his foe more fiercely should pursue:
That > [So that]
5 Who, when his uncouth manner he did view,
uncouth > bizarre; unseemly (i.e. riding backwards and varying his speed)
6 He gan advise to follow him no more,
gan > did advise > bethink, purpose; hence: decide
7 But keep his standing, and his shafts eschew,
keep his standing > [stay where he was; or: hang back] shafts > arrows