That's weird, I don't see my post. Good thing I saved it:

I'm coaching my son's baseball team.

We have a playoff system. 5 teams are involved. They each play one game against each other. So each team plays 4 games total.

Teams

A
B
C
D
E

So, Team A plays four games, against B, C, D, E. Etc.

The TOP TWO teams, based on record, move on. So, obviously if you are 4 and 0, you move on. If two teams are tied at 2-2 for one of the slots, there are tiebreaker criteria (head to head, runs allowed, etc.).

There can be no ties, they all have to be played on the field until there is a winner.

I have heard that if you win 3 games, you are guaranteed to move on, i.e. you will be guaranteed to be in one of the top 2 slots.

Mathematically true? Or is there some scenario where the fourth game would matter to a team that is 3-0?

I can't show my math, but just eyeballing it, it seems that 2 teams could have a 3-1 record.

But there's no way that *more* than 2 out of the five could have a 3-1, or better, record.

3 teams can be 3-1. Basically, for 3 teams to go 3-1, one team has to be 0-4 and the other 1-3 (with the win against the 0-4 team). So, if either the 1-3 or 0-4 team(s) beat one of the other 3 teams, then there will only be 2 3-1 teams. I can make an excel sheet to describe this if you need. If you just want a simple answer, then there will MOST LIKELY be just 2 teams with a 3-1 or better record.