From The TimeSplitters Wiki

Melon Heist is one of the "Monkeying around" challanges for Timesplitters: Future Perfect. In the challange you play the role of an elite henchman, who must snipe watermelons off the heads of monkeys who are walking around the dorms area of Russian Connection, from the water tower. Each sucsesful hit gives you 100 points, whilst every time you hit the monkey instead, you loose 150 points. Combos can be performed by hitting two watermelons in a small frame of time (hit one right after the other.) The combo gives the player 300 points. Further combo scores are possible, when more then two melons are hit in quick succesion.

Melon heist is very simular to Monkey Mayhem of Timesplitters 2.

The scores needed to sucsesfully pass Melon Heist are bellow:

Bronze: 750
Silver: 1200
Gold: 2000
Platinum: 2400