I have heard fathers and coaches yell out commands to their sons and players for quite a few years now. Many times their information is incorrect. One command in particular that stands out in my mind (because I hear it so much) is the one telling the hitter to keep his back elbow up. I’m not sure where this tip first came from, but I can tell you that it is not exactly a “fix.”
With the back elbow up in the air it changes the hinging of the wrists during the swing. Can you see this in the picture? This, in turn, changes the path (see section on swing plane) of the bat, as well as the leverage which affects the speed of the bat. The wrists work much better in the swing if they are slightly hinged back toward the forearm as in the picture to the right.
The proper advice, which may have gotten lost in translation years ago, is for the batter to make sure his back shoulder is slightly higher than the front. The forearms should actually be in a reverse “V” and somewhat close to the body. This allows the bat to flow freely to the ball and maintains a short, compact swing.
Of course, as with all hitting instruction… nothing is a hard fast rule. It can be debated that plenty of Major Leaguers have their elbows up. This may be true, but they are Major League players with Major League bodies. If you are teaching a young player, this is the safest and most practical starting point.