User blog comment:SpaceManiac888/Rusty Spanner of the Episode: Series 10, Grand Final/@comment-25770073-20171203213543/@comment-2118191-20171203215806

Hanging back is actually quite a common tactic in rumbles like that. I've seen in BattleBots where a robot will sometimes just hold off for a while and then come onto the attack - usually it's to conserve battery power. Especially as rumbles have much longer time limits (or none at all in this case) than the regular three minute fights.