you know ... stuff where you get whacked and or the idea is to knock someone out or break bones. These should be avoided, or practiced with a little consideration (good general advice if you ask me warfarin or not)
Contact is defined as :
but perhaps less obviously this is probably not a contact you'd be worried about (with respect to warfarin)
personally if I hadn't damaged my neck in a motorcycle accident in the late 90's I'd probably still be doing Aikido ... but I tried it again and without really close attention to warm-ups and technique rolls (ukemi) were prone to giving me a sore neck which took a few weeks to undo
so while a brave man loves the feeling of the elements on his face, a wise man knows when to get out of the rain.
Train and practice as if you love your body and know spare parts are often "back ordered"