That’s where the book comes in, because the duel between Harry and Snape in HalfBlood Prince is much more interesting when you pay attention to what Snape actually does.
The moment Harry arrives, Snape immediately turns to face him and his reaction makes it clear that Harry was never supposed to witness what had just happened. When Harry starts attacking, Snape doesn’t duel like an ordinary opponent. He reads Harry’s movements, counters his spells effortlessly, and repeatedly demonstrates the enormous gap between their skill levels. The important detail is that Snape is not simply blocking Harry’s attacks; he is controlling the entire encounter. He knows Harry’s spells, anticipates his next move, and can neutralise him without resorting to the kind of aggressive magic Harry expects.
And that raises the fascinating question about Harry being sent flying. A wizard doesn’t necessarily need to shout an incantation to perform magic. Nonverbal spells are a recognised part of advanced wizarding, and Snape is exceptionally skilled at them. In the book, Harry’s attacks are repeatedly countered, and Snape even uses Harry’s own spells against him. However, we should distinguish what the novel explicitly describes from what the film visually suggests: if Snape sends Harry flying without a clearly identified incantation, that does not automatically establish that he used a particular named spell. The point is that Snape’s superior control of magic allows him to defend himself and overpower Harry while barely appearing to exert himself. Harry is fighting out of anger; Snape is fighting with experience, precision, and complete awareness of his opponent’s limitations.
Immediately Snape heard Harry's voice he turned around in haste, he didn't want Harry to be here atall.
The first spell hat Harry casted snapped blocked it, the second one Snape deflected it back at him, that wasn't a block he literally flicked it back Harry's way, cause sape didn't say a word so why was Harry flying?