Why does it say "v'Eleh Mispar ha'Giborim"?
Malbim: Sefer Shmuel mentioned only the most famous ones. Ezra teaches that there were also others.
Why is he called here "Yashav'am ben Chachmoni", and in Shmuel II, 23:8 "Yoshev ba'Sheves Tachkemoni"?
'Rashi', Radak: His father was Tachkemoni (this is the same as Chachmoni), like it says here; these are the same. The son's name was Adino (like it says there).
Radak (Shmuel II, 23:8): There, "Ben" is like 'Ish', like 'Ben Chayil.' I.e. he was a man of Chachmah.
Vilna Gaon #1: His father was "Yoshev ba'Sheves Tachkemoni" (a Chacham).
Vilna Gaon #2: Perhaps "Yoshev ba'Sheves Tachkemoni" refers to both the father and the son (they were Chachamim).
Malbim: There it teaches that after killing 800 in war, his mind was sound, and he would teach Chachamim. Ezra taught here additionally that he was called Yashav'am Ben Chachmoni (refer to 11:11:3:2).
Why is he called "Yashav'am"?
Radak: He was Yoshev (sat) with the king (he was among his advisors) in front of the Am, or about matters of the Am.
Malbim: Due to his Chachmah, he sat in Yeshivah and taught Chachmah to the nation.
Why is he called "Rosh ha'Shalishim"?
'Rashi': He was head if the Giborim. This is like "v'Shalishim Al Kulo" (Shemos 14:7).
Rashi (Shmuel II, 23:8): He is a father (head) in beauty, Chachmah and Gevurah, like it says "Nevon Davar v'Ish To'ar" and "Gibor Chayil" (Shmuel I, 16:18).
Radak (Shmuel II, 23:8): He was the head of three Avos.
Radak (Shmuel II, 23:8) #2: He [sat among the Sanhedrin and Chachamim, and] was the head of them. Shelishim is an expression of grandeur and honor, like "ha'Shelish Asher la'Melech" (Melachim II, 7:2) and "u'Mivchar Shalishav" (Shemos 15:4).
Malbim: He was not head of the three Giborim, for Avishai did like him, and it says that Avishai did not come among the three (verse 19)! Rather, he was head of 30 Giborim listed below, who were at a lower level than the first six. He was the biggest Chacham of the first three.
What is the meaning of "Orer Es Chaniso Al Shelosh Me'os"?
'Rashi': When he fought, he would not return until he killed 300 with his spear.
Malbim: Once, he killed 300 at once, and his hand was not weary, rather, he was able to wave his spear easily to and for.
Here it says that that he killed 300 at once. In Shmuel II, 23:8 it says 800!
'Rashi', Radak #1: One of these refers to the father ('Rashi' - 800), and one refers to the son.
Radak #2: There were two wars. In one he killed 800, and in the other, 300.
Malbim (Shmuel II, 23:8): Here it teaches that after killing 300, he would wave his spear easily to and fro. There it teaches that after killing 800, he investigated deeply in Torah.
