The head; or, heads; the singular number put for the plural, as is frequent. By which he understands either,
1. Their politic heads, their chiefs or ringleaders, who were most malicious, and by whom all the rest were supported and stirred up: or,
2. Their proper and natural heads, as this word is used Psalms 140:7; and this covering of their heads here is opposed to the covering of David's head there. Let the mischief of their own lips cover them; let the mischief which by their calumnies they design against me fall upon themselves.