How would you make a “field” react to someone passing through it, in After Effects only?

Live-action shot, mostly locked off. A runner passes between two posts. I want some kind of field or energy plane to appear in that gap, and as they go through it, it reacts. It could ripple, part, break, scan or light up. I’m open on the look.

It doesn’t need to be a real simulation, just something that convincingly feels like it’s responding to their body.

Any ideas? I know this is possible in 3D software with cloth sims but I don’t have the time for this - quite a tight deadline.

Thanks a lot guys.