Can a manager reduce or "siphon" team bonuses?

Just received notice for this year and I was shocked. Our annual bonus is based on 3 multipliers. One of those multipliers is determined at the manager's discretion.

This year, that multiplier came in extremely low at 50% less than last year across the team. Nothing else materially changed in our performance metrics. We even have 2 vacant positions in the team.

We have a new manager, but he's not new to the team. He's been with us for quite a while and was promoted into this role. This is his first performance review cycle.

I'm not looking to start any conflict. I might even be wrong for assuming this. But I’m just trying to understand if this is even something a manager can do?