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).The feature was added because normally this does happen in the normal OS, but Mac disables this feature for games because many games, FPS for example, use the control key. Some people, not realizing that this conflicts with sprinting with control, requested that Minecraft add the feature to the game. BUT THIS FEATURE IS ABSOLUTELY OBNOXIOUS. Furthermore, the control + left click thing DOES NOT happen on Windows because IT WAS NOT ADDED IN 1.6. If you want proof, here's the 1.6 change log where the "feature" (aka annoyance) was added. Look at the 4th bulletpoint. It says it right there. It was added. Do you believe me now? https://mojang.com/2013/07/minecraft-1-6-2-pre-release/