Algorithm

Algorithm for Players Scores
Repeat until all a players scores have been recorded
  Get points scored in game ( for )
  Get points conceded in game ( against )
  Add the difference to list ( for - against )
When all scores have been input

Set Difference, games_played variables to 0
For each item in the list
  Add its value to Difference
  Add 1 to games_played

When all items in the list have been processed

Print players average ( Difference )
Print their best win is Max value in list
Print their worst defeat is the Min value in list