pin down

verb4

1. •
   To attach or secure with pins.

   • Pin down the tablecloth, so it doesn't blow away in the breeze.
2. •
   To identify something (e.g. a decision or plan) clearly or specifically.

   • Something is wrong, but I can't pin it down.
3. •
   To corner somebody in order to get a firm answer.

   • Let's try to pin him down on a price.
4. •
   To hold the opponent back-first so both his or her shoulders touch the mat or ground.