During PvP Tournaments, Tournament Points are awarded according to the strength and number of Units your armies defeat.
Defeating stronger Units will earn you more Tournament Points. There is little benefit to destroying small, weak armies, as you will not receive enough Tournament Points to achieve a good Ranking position. A better strategy is to find opponents of a similar strength and test your strategy - you will earn more Tournament Points and better Rewards as a result.
When multiple players defend a League Fortress, Beacon or Castle simultaneously, Points are awarded depending on how many of the enemy's Units were destroyed by each player in the defending army.
The Battle Reports for this type of battle will provide you with a breakdown of how each player's Units performed. Players whose Units destroyed more hostile Units will get more Tournament Points, while players whose Units contributed less will gain fewer.