What is "Vala"?
Radak: It is destruction. His words destroyed Achimelech and his family.
What does the verse say about "Leshon Remiyah"?
Radak: You love also this. The Leshon ha'Ra was from when he saw the matter. Had he stopped Achimelech when he saw the matter, and told him that it is evil in Sha'ul's eyes to give to David food and the sword, Achimelech would have refrained 1 ! Rather, Do'eg hid his tongue in guile, in order to slander Achimelech.
Malbim: You are Leshon Mirmah, and caused your own demise via it! Chazal 2 say that Do'eg was the Ger Amaleki who told David that he killed Sha'ul (at the beginning of Shmuel II), to find favor in David's eyes. David said "Damcha Al Roshecha
If David would deny it, why would Achimelech believe Do'eg more than David? Even if amidst Safek he would not give to him a sword, would he let David die of hunger?! Perhaps he would believe Do'eg due to Raglayim l'Davar - why would Sha'ul send David alone, without food?! (PF)
Pesikta d'Rav Kahana 3, Tanchuma Ki Setzei 18.
