Defence against a Jab
I know this may put some noses out of place, however, how many people who have answered this thread box or have boxed? The reason I ask is that some of the answers seem a little naive ( I box );
There are several posiibilities... You deflect the jab with the "same side" hand while doing an atemi on the inside with the cross hand. You can deflect with the same hand and deliver an atemi with the same side hand. You can both deflect and atemi with the same side hand (my preferred method (this is a Wing Chun Jeet Chun Choi I believe) this allows you to trap with the cross hand.
Now it seesm George has worked on this and I am sure it works for him but for those who have never tried this and then to try it for the first time against a boxer will get very hurt. As a boxer you develop automatic responses to being struck, you strike back. The jab is a feeler it isn't mean't to damage but to open up to bring about a droppong of the other fella's guard very often I am looking for my opponent to react to the jab as it will expose him in some way. Also boxers always always use combinations and what starts these comboinations is contact. I throw a punch I feel contact I throw another punch I feel contatct I throw another punch so deflecting etc will only bring about another punch ( a more commited attack which we are use in aikido ). Most trainers will teach you to "slip inside" an opponents guard; A jab is thrown don't try to touch it slip to the side/under it and throw a punch of your own. This has many advantages first of all the counter comes as a bloody big surprise! and since I ahven't hit anything with my jab I haven't even started with my follow up. In my oponion this is the safest but the most difficult way to deal with a jab. You really need to get in the ring and learn to "read" the jab.
Now most people here, I am sure, don't want to get into the ring and have no experience facing boxers. As an aikido-deshi my advice to them is very simple. TAKE THE JAB!!! put your habds up and take it on your hands and close the distance. This isn't hard, everyone has seen two boxers hugging in the ring, this is what you must do. Imagine what you could do from behind a boxer. You will take some shots on the hands as you step in, since the boxer is in jabbing range he is only a step away. Circle to the side to negate one of his hands and step in to negate both of them you can't box from here but you can do aikido at this range.
One word on ma-ai fighting ma-ai it one arms length away the same distance you need to be if you are going to apply atemi or shomen etc. It is very close alot closer than expected in my opinion.