What is the meaning of "Harari"?
Rashi: He was from the mountain (Targum Yonasan - Har Tura'ah).
Why does it say "la'Chayah"?
Rashi: [They gathered] to a troop, like wild animals.
Radak: It is an open city without a wall. This was in Efes 1 Damim (Divrei ha'Yamim I, 11:13).
There, the verse says Pas Damim. In Shmuel I, 17:1, it says Pelishtim camped in Efes Damim when Galyus taunted Yisrael. Rashi in Divrei ha'Yamim says that they are the same.
Why does it say in Divrei ha'Yamim I, 11:13 that the field was of barley?
(Rav Huna) Bava Kama 60b: There were stacks of barley and of lentils. Radak - the field was already harvested. The stack of barley and lentils were from other fields. In each place, the verse mentions one of them.
Radak (16, citing Bava Kama 60b): There were stacks of barley of Yisrael, and stacks of lentils of Pelishtim.
Radak (16, citing Yerushalmi Sanhedrin 12b): This occurred in one year. One field was full of barley, and another field was full of lentils.
Radak (16, citing Yerushalmi Sanhedrin 12b): This occurred in two years. In one year, the field was full of barley. In the other year, it was full of lentils.
Malbim: Elazar was in the barley field, and Shamah was in the lentil field.