Be aware of the reactive forces of a saw. When you cut with the bottom of the bar, the chain can pull you into the work. When cutting with the top of the bar, it can push you away from the work. Your body stance and grip are determined by which part of the bar you are using.
You can experience a kickback almost every time you use a chain saw. Most are easy to control. But a severe kickback can cause one of the worst accidents you can have working with a chain saw. Kickback happens when the chain saw is suddenly thrown violently back towards the operator. It can happen while removing limbs from a tree that is on the ground or while cutting the trunk (bucking).
Kickback occurs when the chain is suddenly forced to stop. The most common way this happens is when the upper tip of the bar touches a tree, log, or branch. Another way the chain can be stopped suddenly is when a log or a limb pinches the top of the bar and chain while cutting from below with the top of the bar. Here are ways kickback can be prevented:
• Keep upper tip of bar in solid wood.
• If cutting a log from below, do it in two stages: ﬁrst cut from above, then make another cut from below to meet the ﬁrst.
• Hold the chainsaw with both hands.
• Grip the handle by putting your thumb around it.
• Keep your elbow locked.
• Never cutting above shoulder height.
• Keep the saw close to your body.
• Using a saw with chain brake.
• Starting every cut under full throttle.
• Keep the chain sharp.
From U.S. Forest Service's: Backyard Woods - Work Safely With a Chainsaw