It's antisemitic because of the use of the term "gagged" which alludes to a Jewish conspiracy that goes beyond the topic at hand and is used to blame the Jewish people for all sorts of wrongs in the world.I don't see the Tweet in question (despite my issues with them misusing the Zionist term) as Anti-Semitic, rather their issue is over both Israel's recent actions against the Palestinians and in relation to attempts by some to shut down fair criticism of the Israeli Right by accusing said critics of being Anti-Semitic.
Likewise while I do disagree with those among the Black Lives Matter Movement that want to "Defund/Abolish the Police", I don't really blame them for holding such a view. What I do feel however is that their focus (on both sides of the Altantic) should more on encouraging more Non-Whites to join the Police, for the Police to take Bigtory of all kinds more seriously (and to be given more resources to stop it) and for any Bigots within our Police Forces to be kicked out of said forces. All those measures would be far more effective at reducing Racism on both sides of the Atlantic compared any attempt to "Defund/Abolish the Police.
I don't blame them either but it's a pretty radical position to take and one which I don't think the Premier League should be promoting by having the name of the movement that supports these positions on the backs of football shirts.