I'm sorry, but changing rules after the season starts is wrong. It is so wrong that the only way it could ever be right is for the league to UNANIMOUSLY decide that they want the change.
Streaming is part of the game. If you don't cap the moves before the start of the season you CANNOT cap them after the start. It is not within your rights as commissioner.
This shouldn't even be a debate. There is no legitimate counterargument.
A guy drafted to be a streamer in a league with no moves limit. If you wanted to foil that strategy, you had to disclose as much before the draft, END of story.
Ditto... if this is a "competitive" league, where people are going to try their hardest to win, they're going to exploit so-called "loopholes" like this. If everyone knows about the rules ahead of time, this isn't angle-shooting, it's strategy
. Plain and simple, it's completely within the rules of the league (as they were set up), and it's a valid plan.
As the commissioner, it's your job
to close the loopholes you don't want before the season, and create a league setup that encourages play as you see fit. If you don't want people streaming, you could put a cap on moves, you could add a bunch of negative and averaging categories, etc, etc, etc. This is simple, basic, commissioner stuff. If you're lazy and just throw a league together without looking at any consequences, of course
there's going to be loopholes, and of course they're going to be exploited... that's how competitive people compete.
Some leagues are going to be offense-heavy, is it unfair if one owner notices this before the draft and spends his first 12 picks on offense? Some leagues have very few counting categories for pitching and no SP-only slots, is it unfair for an owner to draft no starters and only closers? No... it's strategy
. Forming your team based around the defined rules of the game. Simple as that. If the commish isn't smart enough to resolve these things before hand, he probably shouldn't be the commish. If the rest of the owners aren't smart enough to find their own strategy, and draft teams straight off the Yahoo!-board, that's their fault.
Now, if this is a "friendly" league, maybe the managers in question would be willing to tone it down, for the sake of the friendships and fun of the league, and will listen to reason without the rest of the league resorting to changing the rules mid-stream or abandoning the league altogether. If this is truly a friendly league, changing the rules shouldn't be necessary, as the owners in question will agree that they need to calm it down.
Changing the rules of the game in the middle of the game is absolute garbage. This falls entirely on the heads of the commish in my opinion.
As a commish myself, I'm proud of the fact that I spend a lot of time creating a balanced rule-set for my league, and that so far no owners have been able to create an advantage for themselves by thinking outside of the box. I've got teams punting saves, teams streaming, teams loading up on relievers, etc, etc, and none of them have created an unfair environment in my league yet, because I put in the fore-thought and effort before the season to put together the right categories, position spots, innings-max, etc, etc. There's a lot more to this job than just signing people up before the draft.