The Sepoy Mutiny, also known as the Indian Rebellion of 1857, began in Meerut on May 10, 1857. Here's the reason for the outbreak of the mutiny in Meerut:

Discontent among Sepoys: The mutiny was triggered by a combination of factors, including growing discontent among Indian sepoys (Indian soldiers in the British East India Company's army) due to various grievances, such as the use of new rifle cartridges rumored to be greased with cow and pig fat, which offended both Hindu and Muslim sepoys.

Mutiny Spreads: On May 9, 1857, Indian sepoys in Meerut, who were stationed there, refused to use the new cartridges, and they were subsequently court-martialed and imprisoned. This, in turn, led to a larger mutiny on May 10, 1857, as their fellow sepoys rebelled against the British authorities.

Spread to Other Regions: The mutiny in Meerut quickly spread to other parts of northern India, including Delhi, and it eventually evolved into a widespread rebellion against British rule, involving both sepoys and civilians.

So, the correct option is [4].