The gravitational force of a Black Hole, would be the same as the solar mass it was formed from, as it contains the same mass.
I'm sure the event horizon would be massively bigger than a football.
If a Black hole did go to the earths centre, it would increase its mass, thus increasing its gravitational pull, thus it would pull in more mass etc. etc. until the Earth was consumed.
A one solar mass black hole's gravitational pull would extend over the same area as the sun's does. The event horizon is the point of no return, where even light is not fast enough to escape once it has been crossed, I can't remember which book it was, but one of them by some famous scientist (it might have been Hawking's brief history of time)did say that it would be about the size of a football for a solar mass black hole. The extra mass from swallowing an Earth sized object wouldn't increase the event horizon by any noticeable difference, coinsidering it already has the mass of a star.