I'm with you - my almost 6 mo old starting kicking and whacking about six weeks ago and it has gotten gradually worse. He always lightly tapped me on the chest with his fist but now it is full on punches that can take my breath away. He kicks off of whatever he can reach and pushes his whole body around, taking my nipple with him. It is killer. The icing on the cake is that he looks up at me with a big giggling grin as he does it!!!
Anyway, what works for me is to minimize distractions as much as humanly possible. The slightest noise will set him off. Also, as often as possible, I feed him when he is totally relaxed, sleepy if possible. If I can catch him just as he is waking up from a nap, I will "trick" him into nursing. When he's that relaxed, he will always take the breast if I nudge his nose with my nipple and then he nurses calmly and cuddly like the good old days. I'm not sure if this is a good habit to get into but so far there haven't been any consequences (ie. he doesn't wake up and scream when there isn't a boob in his mouth).
I hope this is a stage they outgrow!
Happy mumma to my boys Henny Tom (Nov 30, 2008), Arlo Odie (Oct 5, 2010), and baby SISTER! due mid-Dec 2014.