It's not so much that they're 'dropping' Umbro, Nike themselves own Umbro and are actually phasing the brand out in preparation for selling it, they're transitioning old Umbro teams to Nike kits before they do so.
That, in of itself, is outrageous. Buy an iconic brand, keep up the pretence of caring about it only to take over all of it's sponsorship deals, gut it of said sponsorship deals, and sell it on to someone mad enough to pay for a brand bereft of any clubs to kit out.
If that doesn't constitute a 'hostile' takeover, I don't know what does.
edit: Upon further research, I've discovered that the deed has already been done and that they sold the brand off in December. I'm still certain that my description of events rings true, and that the high profile Umbro clubs and nations were 'induced' to switch to Nike, but I stand to be corrected if anyone has a better grasp on the situation that I.