Ummm...A lil more description? What does the boxing stance look like? Where are your arms? Are your knees bent? What arm did you swing? At what angle from your initial stance...that's what you should include. It may sound complicated but its not. Come on MSN btw...Ill tell you what LoK told me that'll make tai alot easier to explain...
As you swing your arm, Aizen extends his corresponding hand out to meet your fist, and opens his hands so that your fist collides with his palm. As soon as contact is made, Aizen closes his hand around your fist, effectively catching your punch. After catching, Aizen swings his arm to the left, deviating your arm to the left, throwing you off balance a little bit and exposing your chest. Aizen bends his left arm, and performs a chopping motion, driving the side of his knuckles into your upper left arm.