Danny Harriman would stand off back in the audience and throw chalk at him.This will sound cynical, but I imagine there'd be a dozen creative ways to subtly shark John while he was playing, if he showed up . . .
. . . and John knows that -- sorry and unfortunate to realistically envision this possibility. We've all been around the block in this regard.
Arnaldo
After every shot, Lou would loudly proclaim "Maybe he made that shot, and maybe he didn't"
Earl would go ballistic over something and have the ref in a headlock while John was trying to shoot..
Mike Duschene would be at the next table, loudly chalking his cue. Squeak-aw, squeak-aw, squeak-aw.
Joshua Filler would have Pia moving around so she was always in John's line of sight, smiling at him.
XradarX would take off his Danny Harriman headgear, and sneak around the hall trying to find a fire alarm pull-box he could reach.