What is "Matzav Pelishtim"?
Rashi (Shmuel I, 13:23): They are Netzivim to guard lest people leave the city to despoil them.
Radak (Shmuel I, 13:23, citing Targum Yonasan): It is army officers. Bereishis Rabah (3:6) supports this.
What does it mean that Matzav Pelishtim was in Beis Lechem?
Rashi: The army camped in Emek Refa'im, and they sent their Matzav to Beis Lechem.
Radak: The big camp was in Emek Refa'im, and the generals and a [small] part of the army were in Beis Lechem.
Why does it say here "Matzav Pelishtim", and in Divrei ha'Yamim I, 11:16, it says "u'Netziv Pelishtim"?
Radak: These are the same. Also Yonason translates both of these the same. They are generals of the army.