Storm Damage ( also known as Wind Damage)
This is when the tree has been affected by very strong winds which has blown the tree from side to side in a very excessive manor and has broken the cell structure of the willow, it will happen more in the tops of the tree which get whipped around more and therefore it is also more prevalent in narrow grain bats (the grains of a bat are always narrower in the top of the tree than the bottom). If you imagine the cell structure of a willow tree running from top to bottom, if there is lateral movement to excess these cells will break and cause a weakness.
This wind damage is a natural occurrence and there is absolutely nothing us or the bat manufacturer can do about it. The majority of these bats are found when they are in the manufacturing process but some will still get through to the customer. They will not always break ( they normally break as per the attached photo by snapping across the grain) but if slightly misused or they catch a fast Yorker on the toe with perhaps a poor quality ball they are more likely to break. A good way to reduce the chances of this are by having extra toe protection on the bat.
You can see from the photo that storm damage is obvious as the bat will split right across the blade (across the grain) , or sometimes halfway across.
Recently we saw Mahela Jayawardena and Michael carberry both suffer from this type of break.