how would you fix this?

[umpjayfire]

Sitch

I will try to properly paint this picture
0 outs bases empty...2 man mechanics...obr

F3 is playing about 25 feet behind the bag and BU is slightly further back in A
Lefthanded batter hits a hot grounder down the line, over the base where F3 makes a great diving stop.
BU sees its fair, makes proper voice mechanic (meaning none), and just points with his left arm FOUL....uuuuggghhh....
F3, who has heard nothing, knows its a fair ball and it might be a close play (pitcher didn't cover) and runs to first only to see that the B/R has stopped running. F3 steps on the bag and the BU takes a couple steps toward the base and gives an out mechanic....

COMMENCE CRAPHOUSE

I am UIC and ,without being asked, walk up the 1B line to talk to BU who has just said, "What the hell did I just do?" loud enough for the offensive dugout to hear...needless to say he was embarrassed....
If anyone cares I will tell you how we fixed it later but I am interested in how you guys would have fixed it.
Stay with out or call it a foul ball?