Sasuke has always been extremely skilled at taijutsu. Years of time in the Dream have made his taijutsu formidable enough that it is a very bad idea to get too close to Sasuke. Kakashi's just made that mistake, and now he's finding himself stumbled: snagged and tripped right off the branch. But he manages to take Sasuke with him, to some degree. Sasuke tries to slip his legs free, and finds that Kakashi is keeping them tangled up even while he drops from the branch: Sasuke manages to hang on to the branch tightly enough that he isn't dragged down along with his sensei, but he's knocked somewhat off-balance all the same. He has to take some time in which to reorient himself and swing easily back down to the ground, and that is time in which Kakashi can also recover.
Landing lightly on his feet-- no less untidy than Kakashi-- Sasuke doesn't stay still long: there's only a fraction of a second in which Sasuke braces, his entire body coiling like a spring: and then he bolts straight forward in a swift leap, heading directly for Kakashi. And once he's just outside Kakashi's reach--
--he flickers straight around behind Kakashi with blurring speed, skidding slightly in a crouch, and leaps straight at Kakashi's back in a high spin kick with a snap and flutter of clothing. Simultaneously, the sole katana he carries is unsheathed from his back, and as soon as his spin kick completes-- whether it connects or not-- he whips the blade around at Kakashi's waist horizontally, using the momentum of his spin kick to put force behind the slash. It would seem Sasuke has been working greatly on his speed, augmenting it until it is far beyond what he ever reached at the time of his match with Gaara in the chuunin exams. He's also been studying bladework, it seems: realizing that taijutsu and armed combat are some of the only things that cannot be seized and turned against him by Itachi. The average ninjutsu or genjutsu will only hasten his defeat when facing Itachi, so he studies armed and unarmed combat: after all, the worst thing for a Sharingan user is a taijutsu specialist.
The days or weeks (fights and words) of taking Sasuke on have given Kakashi a pretty good idea of how he's improved. Still, those rare moments when he slips enough to let his old student get close to him remain a shock when they occur. As Sasuke dashes about just outside his reach, he hurls the kunai, more as a test of the other ninja's intentions than as anything designed to incur damage.
It never hits Sasuke, instead embedding itself in the ground. Even the foresight of the Sharingan has its limits, after all. Kakashi has a split-second to register Sasuke's intended course. He immediately lunges forward to avoid the brunt of the kick, but Sasuke's heel catches him anyway, and he tumbles forward in a sprawl. He twists just in time to see the phantom trail that the future movements of the katana leave (or will leave) in his vision. Then he's somersaulting away just in time (he can feel the rush of air that the katana stirs up) and finally he's on his feet again--but he's still at the disadvantage here, quite out of breath and disoriented while Sasuke is composed and ready to strike his next blow.
All right. Time for psychological warfare.
Kakashi begins a new set of handseals--one that it may have been quite some time since Sasuke saw last. He certainly never saw it from Kakashi. "Sexy no jutsu!" Clouds billow up around...her, and Kakashiko blows Sasuke a kiss.
Then the jutsu drops and he's gone from sight. The true ninja must be willing to sacrifice dignity in battle.