Learn Turkish: İndirimde kıyafetleri çekiştiren çekiştirene. - At the sale, people are tugging at the clothes left and right.

This idiom uses the subject participle -en ("the one who does") followed by the same participle in the dative case -ene ("to the one who does"). Literally, it's like saying "the one who tugs [is doing it] to the one who tugs." In Turkish, repeating a participle this way is the standard formula to express a chaotic frenzy where everyone is doing the same action at once.

What does the suffix -iştir- add to the verb? Why not just say çeken çekene?

Çekmek simply means "to pull." Adding -iştir- (a form of the reciprocal/intensive suffix) creates çekiştirmek, which means "to tug repeatedly," "to pull from all sides," or "to wrangle over." Using çekiştiren çekiştirene emphasizes not just that many people are pulling, but that they are frantically tugging back and forth, probably fighting over the exact same items.

Why is kıyafetleri in the accusative case if there isn't a normal verb in the sentence?

Even though çekiştiren is a participle acting as a noun here ("the one who tugs"), it retains its verb-like qualities and can still take a direct object. Since the shoppers are tugging at specific clothes at the sale, kıyafetler takes the accusative suffix -i to become kıyafetleri.

Where is the main verb of this sentence?