If the target fails a discipline check (vs. 1d20 + 16), they will be knocked down for one round. Initially a check is rolled to see if the hand "hits" the opponent. This check is 1d20 + casting stat modifier + caster level + 9 vs. the target's AC. If this check is successful, a grapple check is made: 1d20 + casting stat modifier + caster level + 14 vs. a discipline roll for the target. If the caster wins this check, the target is held. Each subsequent round, the grapple check is made again. If the target ever wins the grapple check, this spell changes effect to Bigby's Interposing Hand, applying a -10 attack penalty to the target for the remainder of the duration.
Note: If the target has the "Freedom of Movement" effect, they automatically win the grapple check.