Any chance you dropped a few drops of nute water on that part of the leaf? And, yes, I've proven that to be a sure fire way to damage a leaf.
That explains the localized change in color and sharp margins.
It looks like some of the leaf edges are curling but that could be camera angle so "more information is needed", one, because I'm a hydro grower and pretty new (starting third grow) and, second, nute deficiencies seem not to be a result of insufficient nutrients in the fertilizer or soil but tend to be self-inflicted, ie as a result of lockout.
It would be very helpful if you were to include more pictures of the plant and the grow environment, as well as details about the grow including what soil, feeding/watering schedule, etc. More detail better than less detail.
