This is the current "state" of an NFL game. What does it mean?
3rd and 24 on SF 20 yd
where SF is San Francisco
3rd is third down - you have four downs (plays) to move the ball 10 yards foward, after which you receive another set of four.
24 indicates that you need 24 yards to achieve a first down - obviously a negative-yardage play occurred on 1st or 2nd down.
on SF 20 yd means the ball is currently on the SF 20 yard line, i.e. 20 yards out from the goal line SF are currently defending.
Additionally, If the 'state' is 1st/2nd/3rd/4th down and goal, the offense has advanced to 10 or less yards from the goal line(score). If the offense have negative plays or penalties after this it still says down and goal.