if i could have a punt on any separate part of that, i think lampard to make the assist (given drogba scores first with right foot) at 4/1 would be the most likely to entice me
given it can't be drogba providing the assist, the chances it is lampard are a bit higher than 20% in my (mug footie punter) view - my "pluck a number out of my arse" method has it closer to 26% maybe
thinking about it a little more, maybe you are right - quite a few of lampards assists are probably headed goals, due to the number of crosses he puts in. so once you've got down to it being drogba right foot this pushes "lampard assist" out again
skysports have current season opta stats by team if you're interested:
http://home.skysports.com/optastats....Chelsea&cpid=8