Saikyou no Uta

The Japan under-16 rugby team—nicknamed the Perfect Squad—shattered the power balance of high school rugby after sweeping the world cup. With so many former Perfect Squad members in their home prefecture, Rikuzen High's rugby team has given up all hope of victory and now takes a laid-back approach to training. Enter transfer student and rugby novice Kinzan Yamada. He may be new, but he's ready for the world of rugby. The question is whether they're ready for him...

(Source: MANGA Plus)