I don't think the Nationals had the authority to postpone. When it is the visiting team's last trip, MLB has to give permission. That may have been in part responsible for the delay.
And while that might explain it, I still don't buy it excuses it. Anybody anywhere in any organization should have realized in seconds this game does not get played. As I already said, this is not a "shooting in the city of a sports team." This is literally next door to Nat's Park. And it's DC, Capitol of the US, facing an act of terror. It's not a school shooting in Colorado - any act of violence on this scale in DC is a totally different beast from elsewhere, with a subsequent exponentially larger LEO response/investigation.
No matter how far up the call had to come from, it still should have been near immediate. And I'm not saying that because it was the right thing to do, but rather that it was utterly impossible that there was any chance whatsoever the area would clear out and traffic resume in time for a 7pm game. Nobody could have been stupid enough to think it would have, no matter where they're located.
Crap, we're just gonna be lucky if they don't end up cordoning off the Navy Yard for a five block radius permanently in response to this. I was telling someone earlier, you'd hope the lesson the Feds would learn from this would be that their ridiculous and intrusive security measures don't do diddly squat to stop someone from doing this, they just make it a living hell for the people who aren't crazy/terrorists. I grew up in this area in the 80s and 90s, and before 9/11 you never saw cement barricades and fences around every government installation, and everything was fine.
Heck, I used to eat at the Hot Shoppes cafeteria in Bailey's Crossroads every friday night with my family - the one that was in the DoD/Air Force building? No problem just waltzing right into this military, secure building to eat at the restaurant there. Now? The entire place is fenced off like a warzone, lowering cement blocks in the road, I'd be shot just walking to where we used to park, never mind where the Hot Shoppes once was inside.
But instead, you just know they'll be even more anal about security measures after this, especially around the Navy Yard.