IDIOMS

dig in

(idiomatic) To adopt a resolute state of mind (often: to dig in one's feet, heels, etc.)

Example:   I wanted to say grace before dinner, but the kids were already digging in.
To make a burst of hard work.
  I've got to dig in for a couple of weeks to secure my promotion.
2011 November 5, Phil Dawkes, “QPR 2 - 3 Man City”[1], BBC Sport:
  Mancini's men were far from their best but dug in to earn a 10th win in 11 league games and an eighth successive victory in all competitions to maintain their five-point lead at the top of the table.