He waved the flag and shouted to cheer the team on.
Tips
usage
As nà, 呐 almost never stands alone - it lives inside compounds like 呐喊 (to shout) and 唢呐 (Chinese shawm). The fourth-tone reading is the original verbal sense; the toneless particle reading is a separate, more recent borrowing.
Mouth radical (Kangxi #30) anchors 呐 in the family of voice-emitting characters. Same radical drives 喊, 叫, and 吼 - all things issuing loudly from the mouth.
Right side supplies the sound (内 → nà, with vowel and tone shift). The same phonetic recurs in 纳 (accept), 钠 (sodium), and 衲 (patched garment) - a tight nà-family clustered around this phonetic.