What causes engine to stall when put in gear?

An engine may stall when put in gear due to several factors, including insufficient fuel supply, a faulty ignition system, or a malfunctioning clutch. If the fuel pump is not delivering enough fuel or if the air-fuel mixture is incorrect, the engine can lose power when a load is applied. Additionally, issues with the clutch, such as it not fully engaging or disengaging, can cause the engine to stall. Other potential causes include sensor failures or problems with the transmission.