To catch a tartar means:

Wrong answer highlighted. The correct answer is (c) To deal with a person who is more than one’s match.

Catch a Tartar encounter or get hold of a person who can neither be controlled nor got rid of; meet with a person who is unexpectedly more than your match.
The Tartars (or Tatars), a combined force of central Asian people including Mongols and Turks, established a vast empire during the Middle Ages under the leadership of the warlord Genghis Khan , and were a byword for ferocity.