This was the battle that ended the major career of William Wallace as Guardian of Scotland. The Scots formed their tightly packed spear squares, called schiltrons, with their own archers and some light cavalry outside the squares. That was a mistake. The English under Edward I, as customary in that period, charged ahead with their heavily armored cavalry. The English armored could do little against the schiltrons, but they ran off the the light Scots cavalry and support infantry. That allowed the English to bring up their archers, who proceeded to decimate the Scots at a distance, allowing the cavalry to mop up and chase off the remaining Scots spearmen.
From The Great Warbow: