Is it offensive for sports teams to use Native American names and mascots (SSR)

I don’t think that it is offensive for sports teams to use Native American names and mascots for a couple of reasons. One reason is because the sports team that is using the Native American name or mascots (the Redskins) could’ve asked before using it. Or they didn’t ask they could still use it because it isn’t against the law, but how does it make it offensive? It’s only offensive to me if they slandered (made fun of) the name or whatever they are using. I like that that is one of the few reasons that it would be offensive to use Native American names. Also, why would anyone consider it offensive to use Native American names? I would think that a specific tribe name that a team uses is pretty happy that their name or mascot is being used for something other than in their tribe. But, I can see how people would think that using Native American names is offensive.