The practice of Vattakirutar as mentioned in Sangam literature refers to a king who, when defeated in battle, would commit ritual suicide by starving himself to death. This was a custom among the ancient Tamil kings to preserve their honour upon defeat.

Option 1 suggests kings employing women bodyguards. This is incorrect because Vattakirutar specifically refers to a self-destructive practice among defeated kings, and it has no relation to female bodyguards.

Option 2 suggests learned individuals gathering in royal courts to debate religious and philosophical topics. This is also incorrect, as Vattakirutar does not refer to intellectual gatherings but is a practice related to warfare and defeat.

Option 3 suggests young girls guarding agricultural fields by driving off birds and animals. This again, is irrelevant to the concept of Vattakirutar which is strictly associated with kings and their code of honour in warfare.

Hence, the correct answer is option 4, which accurately describes the practice of Vattakirutar.