What:
A player on offence is chasing after a long throw and is tripped over, while running, by the defence. It is unclear if the offence player would have been able to get to the disc had there been no foul.
Result:
If the offence player believes the defence initiated the non-minor contact they can call a foul. If the defence player accepts that they fouled the offence player, but they do not believe the offence player had a reasonable chance at catching the disc, they may invoke rule 16.3 and try to seek agreement that the result of the play should stand. If the players cannot agree what would most likely have occurred in the play, the disc must be returned to the thrower and the players return to where they were when the disc was released (rule 1.12 and 10.2.2 ).

Extra:
If it is clear to other players that the offence player did not have any chance at making the catch had there been no foul, they should encourage the offence player to let the turnover stand.If the foul is accepted and it is agreed that it did affect the play, the offence player gains possession where the foul occurred, not where they would have caught the pass.A receiving foul can be deemed to have occurred if any player involved in the foul is attempting to make contact with the disc in anyway i.e. to catch it or block it.Non minor contact that occurs directly after the attempt at the disc (i.e. a defender catches the disc and then collides with an offence player) is considered to be a receiving foul. However contact with the opponent’s arms after the block occurs is not a sufficient basis for a foul as per rule 17.2.1.1.If Player A initiates contact with an opponent (Player B) that is the cause for Player B contacting Player A’s teammate (Player C), then Player C cannot call a foul on Player B as they did not initiate the contact. If the disc is in the air but the players involved in the foul were running to receive or defend the next pass after possession has been established, this should be treated as an Indirect foul (rule 17.8).An accepted offensive receiving foul is a turnover (rule 17.2.2); however an accepted indirect foul by the offence is not (rule 17.8.2).If players have dived to make a play at the disc, the disc is contacted, but not caught, and then one of the players attempts to make a second attempt but they are obstructed by the player who had dived on the ground, this is not a foul by the obstructing player, unless they deliberately move to obstruct the second attempt (in which case, this could be a violation of rule 12.5.1 even if no contact occurs).