Posted by: mike c. () on Wed Apr 10 14:11:37 2002

No, you are not allowed to block the bag at first base or any other
"base" in the field. Each base is governed by different rules than
that of home plate. This is because you are not allowed to collide
with a fielder. Home plate evolved as fair game in baseball
because the catcher began wearing equipment (i.e. armor),
giving him an edge over the baserunner. This is why collisions
are allowed at the plate. Since the catcher can deliver a blow and
the runner is unprotected, the runner has the option of initiating
the blow himself, as a means of protection.
Since no other fielder in the field wears armor, collisions are not
allowed, therefore, you can't block the bag at first.
Now, all that said, you can strategically place your foot to make it
more difficult for the runner to reach the bag, but you can not
make a concerted effort to block it.