1)
Why was David afraid?
1.
Radak: He was afraid lest they kill him, for he killed their Gibor 1 and many [others] of them. Va'Yira is written with only the Yud due to the conjugation; the Yud of the root 'Yarei' is omitted.
2.
Malbim: Refer to 21:12:1:2.
3.
Above (18:25), Malbim said that surely Pelishtim will hate him and find a way to avenge him for disgracefully cutting off Orlos Pelishtim, not in the way of war. (PF)
1
Refer to 21:11:2:1*.