Why does it say "va'Yatehu"?
Radak: He tricked Avner; he did not realize that Yo'av comes to kill him.
Kli Yakar: He [judged Avner like a Sanhedrin, and] tilted the verdict. 1
What is "El Toch ha'Sha'ar"?
Sanhedrin 49a: He judged Avner like a Sanhedrin for killing Asah'el.
Radak: It is the gate of the city Chevron.
Radak, Abarvenel: This is like "ha'Sharah El ha'Zekenim" (Devarim 25:7. Why do they bring a verse about Yibum, for which a Beis Din of three suffices? They should have brought "El Ziknei ha'Ir ha'Sharah" (Devarim 22:15), regarding Motzi Shem Ra, or like Rashi and Yad Ramah say there, "El Ziknei Iro v'El Sha'ar Mekomo" (Devarim 21:19), regarding Ben Sorer u'Moreh. Those require a Sanhedrin of 23! - PF)
If the Sanhedrin truly judged him, why was David so upset? Really, the Sanhedrin could not execute him, for he was not warned. If a Chacham need not be warned (like one opinion in Sanhedrin 8b), perhaps there were not two witnesses; Sanhedrin cannot execute through Avner's admission. In any case they could rule about Avner's defense that Asah'el was a Rodef (refer to 2:23:4:1). If they reject it, it is reasonable for the king to use his authority to kill if he deems that the situation requires this. (PF)
What is "ba'Sheli"?
Rashi: It is b'Shogeg. Avner did not know that Yo'av comes to kill him. The verse should be re-arranged; Yo'av made him veer b'Shogeg to the gate, to speak with him.
Radak #1: It is b'Shalom (peaceably), like "Yishlav Ohalim" (Iyov 12:6).
Radak #2: It is suddenly. Targum Onkelos of "b'Fesa Pis'om" (Bamidbar 6:9) is bi'Skef Shalu.
Radak citing Sanhedrin 49a: He spoke with him about Shalu (removing. Yo'av asked how a woman without hands does Chalitzah (removes the Yavam's shoe). Avner bent down to demonstrate (i.e. with her teeth). Yo'av drew his sword and killed him). B'Sheli is like "Shal Na'alecha" (Shemos 3:5). This is why it says [that he killed him] "uv'Na'alo Asher b'Raglav" (Melachim I, 2:5).
Malbim: This is an expression of removal, like "Ki Yishal Zeisecha" (Devarim 28:40). He said that David overlooked something that he wanted to talk about with Avner, and he sent Yo'av to tell him.
What is the meaning of "ha'Chomesh"?
Radak: It is like El ha'Chomesh. There are many verses like this, like I explained above (2:23).
Why does it say "b'Dam Asah'el"?
Radak: He judged Avner like a Sanhedrin for killing Asah'el. Avner said that Asah'el was a Rodef (pursuer). Yo'av said that he could have stopped him by maiming a limb. Avner said, I could not aim so precisely. Yo'av said, you were able to strike the fifth rib - all the more so you could have maimed a limb!
Malbim: That is the only reason he killed him - it was not at all due to suspicion or benefit of the king.
