pot shot

from the GNU version of the Collaborative International Dictionary of English.

• Lit., a shot fired simply to fill the pot; hence, a shot fired at an animal or person when at rest or within easy range, or fired simply to kill, without reference to the rules of sport; a shot needling no special skill.

from Wiktionary, Creative Commons Attribution/Share-Alike License.

• noun A haphazard shot with a firearm, taken with careless aim, often fired at a random target.
• noun A shot taken from a hidden stakeout.
• noun By analogy, insulting or hurtful words carelessly or randomly said; opportunistic attack, especially criticism.