This isn't the answer to your question, but I don't think pushing the net at near ground level would cause much movement at popup height. You just have to affect the net at the height just above the catcher's reach.
Question: if a fan purposefully pushes the net behind home closer to the field of play so that it hits a foul popup that the catcher is attempting to catch is that fan interference?
Earlier this year I asked if anybody had ever won a game while sending less than 27 batters to the plate (not weather shortened). Cubs won't do that today, but it was very close to happening.
If the Cubs keep Arrieta on the same schedule the rest of the season he will face SF, LAD, AZ, STL, PIT, STL, PIT, CIN and then would be due to pitch the WC game with 2 extra days rest.