The Secret Triwizard Challenge

You aim for the spider's legs, and cast Stupefy. Two of the spider's legs are hit, and it crashes to the ground, twitching. You walk into the clearing slowly, working your way around the spider.
The spider manages to get up, though it's a little wobbly. It's even more pissed than before, and you're only halfway across the clearing when it sets its sight on you. Do you fight or flee?