If you are in a sparsely populated area flying by yourself a GA aircraft can absolutely fly 500' over your head.
As for an open air assembly of people...apparently it's 10,000.
Sporting events TFR reissued - Smaller events now excluded
Dec. 12 — The FAA this weekend cancelled the “sporting events” temporary flight restriction (TFR) notam, and then on Monday reissued the notam with exactly the same wording. But AOPA has learned that there was a behind-the-scenes change in interpretation that will benefit general aviation pilots.
The notam, FDC 1/3090, requires pilots to remain clear of “any major professional or collegiate sporting event or any other major open air assembly of people” by 3 nm horizontally and 3,000 feet vertically. But FAA has now internally defined “open air assembly” as a gathering of 10,000 people or more. That means most high school games and other smaller athletic events aren’t covered by the TFR.
“This change of interpretation removes some of the restrictions on pilots,” said Andy Cebula, AOPA senior vice president for government and technical affairs. “However, we will continue to believe that these kinds of TFRs should be date and location specific. Local pilots might be aware of major events, but transient pilots have no reasonable way to obtain this information. We will continue to push FAA to eliminate this ‘generic’ TFR.”