Parashas Behar · Aliyah 1 · Passuk 25:09
Chabad.org — English translation + Rashi
Torah Temimah cites Rosh Hashanah 27b.
English: “And you shall sound a shofar.” It was taught: If one inverted it and blew, one has not fulfilled the obligation. What is the reason? As Rav Masna said: “And you shall sound a shofar” — we require the manner of its natural sounding.
Classical derasha (Bavli Rosh Hashanah).
If one turns the shofar upside-down and blows, one has not fulfilled the obligation, because the verse requires blowing in the natural orientation.