Why Fernando Alonso left McLaren?

At the beginning of the 2007 season, Alonso switched from Renault to McLaren, joining forces with Lewis Hamilton, a rookie. However, it was clear from away that Hamilton was no ordinary rookie as the British driver engaged his teammate in battle both on the track and in the rankings. This resulted in a number of difficult situations, most notably during the Hungarian Grand Prix qualification when it was determined that Alonso purposefully held up Hamilton in the pits to prevent the British driver from beating him to pole position.

Alonso was assessed a five-second penalty when the stewards looked into Dennis' outburst and were captured on camera throwing his headphones. The BBC says that Alonso told his team manager that he had access to emails pertaining to the "Spygate" controversy and that he was willing to submit them to the FIA during a heated exchange between Dennis and Alonso the morning of the grand prix.