3 Whom when the giant saw, he soon resigned 4 His former suit, and from them fled apace;
suit > pursuit, chase apace > quickly
5 They after both, and boldly bade him base,
They after both > [They both went after him] bade him base > challenged (alluding to the game of "prisoner's base")
6 And each did strive the other to outgo,
outgo > {Outdistance; go faster than}
7 But he them both outran a wondrous space,
a > [by a]
8 For he was long, and swift as any roe,
roe > roedeer