Complex sentence: At the start of the season the team was the subject of protest over the use of a "radical" rear wing concept on the Mercedes F1 W03, which was not settled until the third race in China when the stewards unanimously rejected the protest.
Split into simpler sentences: At the start of the season the team was the subject of protest over the use of a "radical" rear wing concept on the Mercedes F1 W03. Which was not settled until the third race in China when the stewards unanimously rejected the protest.