head off

Block the progress or completion of; also, intercept. For example, They worked round the clock to head off the flu epidemic, or Try to head him off before he gets home. [First half of 1800s] This expression gave rise to head someone off at the pass, which in Western films meant "to block someone at a mountain pass." It then became a general colloquialism for intercepting someone, as in Jim is going to the boss's office--let's head him off at the pass.

The verb has one meaning:

Meaning #1: prevent the occurrence of; prevent from happening
  Synonyms: debar, obviate, deflect, avert, stave off, fend off, avoid, ward off