**Answer:** 3.

Since there were 5 teams in the league there were a total of 10 possible games (either way around):

Longton vs Fenton

Longton vs Blurton

Longton vs Hulton

Longton vs Fulton

Fenton vs Blurton

Fenton vs Hulton

Fenton vs Fulton

Blurton vs Hulton

Blurton vs Fulton

Hulton vs Fulton

Since each game distributed 2 points to the two teams there were a total of 20 points available to the league.

The results shown add to 17, leaving the remaining 3 to Fulton.