Onathallu or Avittathallu is a festival celebrated by the Nairs of Pallassana Desham in the Chittur Thaluk in Palakkad district, in the southern-most state of Kerala, India. The festival is a tradition followed by the Nairs of the region in commemoration of the numerous wars they led and fought as part of the army of the Kolathiris. The name Pallassana refers to the fact that the group historically constituted the Pallava Sena or the Pallava Army, which eventually morphed into Pallassana or Pallasena, as it is known today.

The tradition involves an enactment or warlike performances by men of the Nair community at the Vettakaruman Dewaswom temle premises. The key component of the performance involves men pairing up and, under the guidance and supervision of elders in the community, enacting physical combat, war cries and battle-like behaviour. This is seen as a vazhivaadu by the men involved, and is a highly revered and attended festival during the Avittam nakshatra of Onam.