1)
What is "Noveh"?
1.
Radak: It is to Nov. Therefore, the accent is on the penultimate syllable.
2)
What is the meaning of "va'Yecherad"?
1.
Radak: He moved. This is like "va'Yecherdu Ziknei ha'Ir Likraso" (16:4), "Yecherdu ch'Tzipor mi'Mitzrayim" (Hoshe'a 11:11).
2.
Targum Yonasan: He was afraid [Radak - because he came alone 1 ]. Malbim - if he comes for needs of war, soldiers should be with him. If he is on a mission, where are his youths and servants?!
3.
Kli Yakar: He came on Shabbos (Menachos 95b). Achimelech was alarmed - why did you need to be Mechalel Shabbos 2 ? If it is to save a besieged city, there should be soldiers with you!