Silver Discrepancies

So, I just had a game, where yas top was constantly pushing and no one defended. We got to a point where 3 of my teammates were at tier 2 tower defending while yas was breaking nexus towers alone and destroyed nexus, while the teammates were still at tier 2 until they saw him attack nexus.

I mean, it s what the f really how are they silver. It s the most basic thing a player should know, defend the nexus ...

Is this normal riot?