Sentence:  This politic selection did not alter the fortune of the field, the challengers were still successful: one of their antagonists was overthrown, and both the others failed in the “<WSD>attaint</WSD>”, that is, in striking the helmet and shield of their antagonist firmly and strongly, with the lance held in a direct line, so that the weapon might break unless the champion was overthrown. 
Meaning of the word marked with <WSD> tags:  A blow or strike, especially in jousting.