The red area from approximately the hitters waist to shoulders is called the Over Zone or the O Zone.  This Zone can be dangerous but it also can be used to your advantage. It is generally dangerous  when your behind in the count and with off speed pitches but can be used successfully in a number of different situations.

The most common way the O Zone is used is when a particular hitter has trouble lying off of the high-heat at his letters.  After you see the hitter chase the high fastball you can throw the next pitch slightly higher to see if they're willing to chase it again.  Keep throwing the fastball slightly higher and higher to see how high the batter is willing to chase. This strategy of pitch-sequencing is called “climbing the ladder.”   Pitchers with good velocity are more likely to use this strategy more often. 

After throwing two or three high hard fastballs in the O Zone, hitters are set up for the off-speed, which translates to a change-up or breaking ball in the bottom of the Go Zone or 4 Zone. The opposite of high-and-hard is low-and-slow. Using this sequence is an example of changing speeds and Lokations on consecutive pitches to disrupt the hitter’s timing.  It can also be called speeding up the hitter's bat.

It is better to practice aiming at the top half of the O Zone around the hitter's chest.  This is one of the few instances where it can be dangerous to miss down.  4 seam Fastballs in the O Zone will change the hitter's eye level and timing.  Commanding the O Zone will give you a chance at a getting a swing, unlike the Purpose Zone, especially if the hitter has trouble laying off the high heat.

Once you command the O Zone the hitter has tracked and timed a high flat planed fastball.  They know they would need a quick bat and good fastball timing to hit that pitch squarely.  After the hitter tracks the high fastball they keep that timing for the next pitch, so it will generally be harder to time a change up in the Go or 4 Zone afterwards. They will most likely swing early or shift their weight forward early on a change up in the Go or 4 Zone.  This is called speeding the hitter's bat up.   

The O Zone is also very useful for pitchers who throw the 12-6 curveball.  Breaking pitches with heavy vertical movement, tilt, or top spin mostly break within the hallway of the plate to the pitching rubber.  That 12-6 breaking ball has to be aimed in the RB for the pitch to end in the Go or 4 Zone.  Once you command the breaking ball in the Go Zone, you can throw the fastball behind it from the same slot (O Zone) where the previous BB started to break.  Hitter's will see both the fastball and breaking ball in the same spot when the pitch is halfway to them.  This makes timing and pitch recognition difficult. 

There are times to use the O Zone instead of the Purpose Pitch.  You don't always want to throw an aggressive pitch inside off the plate towards the hitter in all situations.  When facing the bottom of the order and ahead in the count, facing a slumping hitter, or have the bases loaded, the O Zone can be used instead of a Purpose Pitch.  It will set the hitter up for an off speed pitch without taking a big risk of hitting them.  Game situations will have a big impact on how aggressive you should be with Purpose Pitches.  Know when to use the O Zone instead!