Rule 12(f) motions to strike are due before serving a responsive pleading. Therefore, they are due no more than twenty-one (21) days after the operative complaint, counterclaim or crossclaim is served. If no responsive pleading is due, Rule 12(f) Motions to Strike are due twenty-one (21) days after the pleading to which they relate. Fed. R. Civ. P. 12(b), (e), (f).
When a defense has no grounds or when there has been something included in the pleading that is inappropriate or has no bearing on the case. This prevents those statements from being entered into official court records.