The Secret Triwizard Challenge

"Reducio!" you say, pointing your wand at the spiderwebs. The spell can't hit your foot because the spiderwebs block your foot, so it's significantly safer than using Diffindo.
The spiderwebs become smaller, hurting your ankle a little in the process as they tighten, then snap, around it. You shake your foot loose.
Now, there's the spider. It's too close for comfort, but you have the option of running or shooting another spell at it. Which do you do?