Mutiny!
Magellan and his crew reached present-day Rio de Janeiro four months after setting sail in January 1520. They sailed south and then west, but reached a dead end. This forced their expedition to continue south. No European ever sailed as far south along the Atlantic Coast of South America - so they had to investigate every single outlet for any possible way through South American continent to the Pacific Ocean. The men were cold, exhausted, and hungry. When Magellan reduced rations, the sailors reached a breaking point. His captains presented him with a petition demanding to return to Spain, but giving up was not an option for Magellan. Lost hope and harsh conditions resulted in a mutiny on March 27, 1520.
As (the mutineers) understood that Gaspar de Quesada was a friend of Magellan's, Juan de Cartagena got in his boat at night, with twenty men, and went to the ship of Gaspar de Quesada... in order that all three might go at once to board Magellan and kill him..."
The First Voyage Around the World by Magellan by Antonio Pigafetta and Lord Stanley Alderley, 1520
Magellan acted decisively to protect the future of the expedition.
"The Captain-major went to the said three ships which were already mentioned, and there the captain of one of them was killed, who was treasurer of the whole fleet, and named Luis de Mendoa; he was killed in his own ship by stabs with a dagger by the chief constable of the fleet, who was sent to do this by Fernando de Magelhaes."
Pigafetta's Logbook, 1520
Magellan blocked the other ships from escaping and quelled the mutiny. This example of leadership proved he could prevail during tough situations.