HuffBet
Suppose a team trails 20-14 and scores a touchdown to tie the game. A successful one-point kick puts it up 21-20. If that is the final score it wins outright, but a -2.5 point spread needed at least a three-point win.
That team needs at least 21 points for the over. A match total adds both scores, so 21-20 puts 41 points on the board.
Start counting after half-time. Subtract each team's half-time score from its score at the end of the stated period, and check the market's overtime wording.