Malbim: It is their leaders, like the coming verse explains. They will be cut off for not teaching them to go in the proper way.

Rashi: It is an expression of kings and rulers. Kipah is an arch. I.e. those who hover over them like an arch. Agmon is a small arch. It is called Agmon because it is bent like an Agmon (hook).

Rashi citing Beraisa d'Shmuel: They are astrologers who prophesize based on what they see in the constellations. Hashem will cut them off [from Yisrael].

Radak: They are the strong and the weak. Kipah is a branch - "v'Chipaso Lo Ra'ananah" (Iyov 15:32). Agmon is a reed that grows in water.

Malbim: They are strong and weak branches, respectively. This is a metaphor for the strong and weak. Also the nation were guilty, like will be explained below (16-17).

Radak: It is the day that the Shevatim ¹ were exiled.