What is this Geis from?
Spoilers for the second half of Fate/Zero:


   After the defeat of Caster in episode 15, Kayneth goes to the church (in episode 16) and asks Kirei's dad for a Command Spell as a reward for having helped defeat Caster (not that he did a damn thing; that was all Lancer). Kirei's dad agrees and gives him a Command Spell. At more or less the same time, Maiya abducts Sola-Ui and also cuts off her arm with the Command Spells. Lancer returns to Kayneth at this point, no longer able to locate Sola-Ui now that her Command Spells have been severed.

 Saber (with Irisviel) happens upon Lancer at this point and they start dueling. Meanwhile, a bit away from the duel, Kiritsugu shows up with Sola-Ui's body and proposes a geis to Kayneth - Kiritsugu will leave Sola-Ui with Kayneth and shall nevermore harm either of them, provided that Kayneth uses up all his Command Spells and orders Lancer to commit suicide. Kayneth agrees, since that appears to be the only way out of the situation, and compels Lancer to kill himself. Kayneth breathes a sigh of relief, since he and Sola-Ui are now safe from Kiritsugu and Saber.

 Of course, Maiya is lying in wait with a sniper rifle, and kills Kayneth and Sola-Ui immediately thereafter. She wasn't bound by the geis, after all. Sucks to be Kayneth.

 In any case, only a few minutes at most pass between the geis taking effect and Kayneth/Sola-Ui being assassinated by Maiya (which renders the geis moot). The geis emphatically was not in effect at any time before that, and as such did not impact Kiritsugu/Saber's previous fights with Kayneth/Lancer.