What:
An offensive player accidentally runs into a defensive player and knocks them over. The thrower has not released the disc. The defensive player calls a foul.

Result:
Play stops. The defensive player makes up any positional disadvantage caused by the foul (Rule 17.8).

Why:
The foul did not occur before, during, or directly after an attempt to catch the disc and is therefore not a receiving foul.

Extra:
If the disc had been in the air when the foul occurred, but the foul did not occur before, during, or directly after an attempt by those players to catch the disc, then play would continue until possession was established. If the offensive team retained possession, the defensive player should then make up any positional disadvantage caused by the foul and play would restart with a check (16.3.2).If the offense commits a foul after establishing possession in the air, but the foul was caused by actions not related to the process of making the catch (eg while attempting to intentionally land in the end zone), this should be treated as an indirect foul.