Complex sentence: A role on "Life on a Stick" was offered to the then-unknown Charlie Day; he turned it down to continue working on the pilot for what would become "It's Always Sunny in Philadelphia".
Split into simpler sentences: A role on "Life on a Stick" was offered to the then-unknown Charlie Day. Day turned down the part in order to continue working on the pilot for what would become "It's Always Sunny in Philadelphia".