anyone have any idea whats wrong? its only on this leaf

You need to give us a lot more information about your grow before we can help. A blurry picture alone isn't enough.

From that pic, it could be ozone poisoning, mites, pH, or any number of things.

Have you been foliar feeding?

a pic of the whole plant would help a bit too.Almost looks like a virus but without a bit more info/pics,its harder to tell.Could also be just a pigment problem aswell.

Could be a number of things except a virus. If it's only one leaf (and isn't spreading), it's most likely not significant.

is it on new growth or on the bottom.....looks like the bottom as its close proximity to the soil....

keep an eye and see if it spreads up the plant.....

whats the ph (soil/feeding)
are all the minerals and nutes supplied?

i cut that leaf off its only on the bottom leafs it weird it killed one other leaf so i will cut that one off as well it seems to have bounced back quickly its growing again so i can;t complain i have no idea soil ph i don;t have a tester for that so i have been using water and half strength nutes ...u can see the plant here..... http://forums.cannabisculture.com/forums/ubbthreads.php?ubb=showflat&Number=1587621#Post1587621

have you been using tap, distilled, or Reverse Osmosis water? looks like you may be seeing the first signs of Calcium and Magnesium defifiecy; more likely than not, due to pH problems, or not adding a Ca + Mg supplement to the water.

Dont worry it could be alot of things just let things be and let it grow. If it continues to affect other leaves then post another pic. I think you did the right thing by clipping the leaf.