Neste caso, sugiro:
- One day I was at school and there was a soccer game happening. I was not participating in the game.
Confira a seguir um exemplo de uso retirado de uma publicação internacional, que comprova o uso de "there was...happening"
para dizer "estava tendo"
"The car was hit so hard it was sent into a ravine and ended up hitting a batting cage at KCK Community College. There was
a game happening
in the baseball facility, but thankfully no one was hurt." (Fox4kc.com
Se você quiser dizer "está tendo (um jogo, etc)"
em inglês, basta usar "there is...happening"
.There's a World Cup happening now.
[Está tendo uma Copa do Mundo agora.]