It doesn't say what the delays are, but I am guessing that Metro is swamped with Rally-goers.
I would guess that’s true. When I was in DC, my friend and I went to an event at Nationals Park (baseball stadium). We left for the stadium hours early. The Metro was packed. I’m sure for this event it will be even more so. Perhaps the authorities will add some trains, but I doubt they can add too many or there would be some real gridlock along the rail lines.
Now the Orange Line is also delayed. It was on time earlier.