>>21163
it depends what you understand form greatest and worst.

By worst I would understand changing the tide of history in a bad way for the particular state.
If this is the case for you I would say battle of zenta or generally ww1.

By greatest I hope you mean solely anatolian Turks because otherwise there are too many. Anyway my bets are on mankizert then miryokefalon. Thanks to the latter anatolia finally became 'Turcia' the named given to our geography by venetians, even today our name Türkiye comes from it.

Besides these Turkish war of independence deserves honoary mention, as we were the last independent Turkish country on earth, we were so close to vanish and become a footnote in history books we had a comeback despite the odds were greatly against us.