Simplify the following text for a Grade 10 native English-speaking person.
Original: The Lookouts drummer TrÃ Cool began filling in as a temporary replacement , and when it became clear that Sobrante did not plan to commit to the band full time , Cool 's position as Green Day 's drummer became permanent .
Simplified: The Lookouts drummer TrÃ Cool became areplacement , and then became a permanent replacement because Sobrante did not want to come back .