Minecraft wiki entry for Things_not_to_do, associated text: If the player hears a creeper's hiss behind them, they should not attempt to turn around and knock it away as it is completely/nearly impossible to kill a creeper at that point quickly enough to prevent the explosion. Sprinting away to attempt surviving the blast should be the player's highest priority, unless they have a shield, which can block the damage from the creeper explosion, in which case they should turn around and use it.