Below is the response from the Maryland State UIC regarding the situation as you have presented it:
There are a lot of if's and judgments involved.
The fielder making an initial play on a batted ball can not be interfered with.
However the rulebook does not give two fielders the right of way.
A judgment decision must be made if the pitcher or the first baseman has the right to the ball.
If it is the First Baseman, then the pitcher has committed obstruction.
But since it was a foul ball, the Batter Runner merely returns to continue batting.
If the pitcher is considered to be the one with a right to the ball, the Batter Runner has committed interference.
Dead Ball, Batter Runner is Out, All other runners return.