Gameplay isn't canon. If you mean the cutscene, he definitely wasn't running.
Seriously though, he might not have known what it was, and in case after he whacked the Chief it came off, and when the Chief tried to get it back he just hoisted him up well away from it, held him over... something, and started choking him (or doing something else unpleasant and presumably deadly).

: Since when has pride been a synonym for 'stupid'?

since always

: OK. Let's think this through. The Didact isn't just a warrior, he's a
: general. He's commanded troops, led campaigns, fought against augmented
: humans.
: And as you put it, he thinks that throwing a Spartan in power armor across a
: room is going to kill him.

: The Didact is an idiot.

What about the part about the slipspace rupture right after that? How about after that when the whole core was falling apart?

: Or how about the rest of his approach to killing the Chief? You mentioned
: that the Didact was at least throwing Covenant and Prometheans at him. But
: he lured the Chief through an entire army of both in order to get himself
: released. And if he bothered to ask Jul to catch him up on current events,
: he'd know just what the Chief accomplished a few years ago.

I figured he was busy. Like you said, he's more of a commander. We have the saying "If you want something done right, do it yourself", but who's to say the Forerunners did, or saw things that way?