A lot of assumptions, because even though you gave a good description there is a lot to fill in:
Fifty feet and closing is plenty close -
1. Change course - cross the street. If they continue to block or prove to be strutting and posturing do an about face providing you are not heading into a "dead end." Further from home is not bad if you can eventually get there.
2. If they are proving that they have intents - just harassing or otherwise, use your phone to call 911.
3. If you continue to feel a threat, while on line with 911, shine light and with a strong verbal command order them to give you space. In EMS we were taught and taught that a six foot radius was "our property," and no one was allowed in that perimeter without our permission. Due to how fast a threat can close distance we protected out to twenty feet.
4. Do not panic, and do not run, unless being chased. Be confident and strong, but do not threaten what you can not promise - if you don't have a gun, don't threaten to shoot. The nice thing about calling 911 first is that when you say the police are on the way ... they are!
5. On your own posture and presence: As Walt Rauch has said - You don't want to be a sheep. You want to be grissle. Stand tall and confident, don't look down or away. Move straight, tall and with purpose. Wolves attack the weak. And as I add - Don't go looking for wolf packs to test this out!
Stay alert, be observant, and stay alert!
I'm sure there will be much more, and I look forward to hearing form Rob and Michael.