Sweep
Journeyman Pro
Is the correct answer.Well, the fourball did have the right of way, didn't they? At least that's the policy on most courses I know. You can tee up on the tenth, but only if you are absolutely certain you don't hold anyone up. That means having a look down the ninth hole and make sure that no one is coming up.
The correct thing would have been grant the fourball their right of way on the tenth and then hope that they would later let the threeball through if they were actually faster (which the four very well might have done, had they not already been so miffed at them for jumping in front of them on the tenth).
Personally, I blame Brexit