Radak, from Sanhedrin 95a: Ish she'Ba due to the destruction of Nov (which came via David; refer to Shmuel I, 22:22:1:1,2).

Radak citing his father: It is a giant, one of the Refa'im; Refa'im can have an Aleph or Hei (after the Reish). Also Yonasan translated "Gibara" (a mighty man).

Radak citing Sanhedrin 95a: She is Orpah (the mother also of Galyus).

Rashi: It is a case at the end of the handle of his spear. It is in the shape of a hat or helmet.

Mahari Kara: It is his helmet.

Radak: It is the stick of the spear. In Arabic it is called Alakanah.

Radak: The blade of his spear. It says "Mishkal Kino" because the blade is with Kino. The verse would not say so about the stick. Also for Galyus, it gives the weight of the blade of his spear - 600 Shekalim of iron (Shmuel I, 17:7). These are not the same as Shekalim of copper. Also gold and silver have different units of weight.

Rashi and Mahari Kara imply that Kino (a case at the end of the handle of his spear, or his helmet) weighed 300. (PF)

Rashi #1: He had a new belt.

Rashi #2: That was the first day he wore weapons. The custom is to make victory and might on the day of inauguration, to acquire fame. Therefore, he wanted to strike David.

Radak: He wore a new sword. The word sword is omitted; it is understood from context. This is like "u'Ma'achalo Beri'ah" (Chabakuk 1:16), i.e. a fat Seh, and many verses.

Refer to 21:16:5:2.

Radak: He saw that David was weary.