Because pressing control and left click in Minecraft on a Mac results in a right click, it is impossible to left click (and therefore break blocks or attack) whilst sprinting. Before you mark this as a duplicate of bug reports claiming that the control + left click = right click does NOT work, let me be perfectly clear : control + left click = right click DOES work on Mac, but the fact that this cannot be disabled prevents you from left clicking whilst, for instance, sprinting with control because it results in being a right click. So, here's my suggestion for a simple fix : in the controls panel of the options on the Minecraft Mac client, add the option to DISABLE the control + left click = right click for the people who do not need it and do not want it for the reasons stated above (because you can use a mouse or click with two fingers on a trackpad to right click anyways).