"Mr J
On another thread,amongst your information was Port Adelaide +26.5 points.
If your system predicts Brisbane between 1-19 "what the?"

Simple. My system predicts Brisbane will win by 1-19 points. So I take the spread (handicap) on Port for +26.5. So if Brisbane won by 1-19 points then the +26.5 covers.

Probally the term 'spread' that threw you off. Remember 'spread' is the same as handicap or line.

Selecting a team to win by a certain margin (e.g. Brisbane by 1-19 points) is margin betting.