Blood Bowl depicts a game of 'fantasy football', akin to a very violent version of American football. It is played with a collection of 28mm models (Citadel Miniatures) representing the two 'football' teams. The board represents the pitch, and, as with most board games, gameplay proceeds using dice, cards and counters.
Strictly speaking, Blood Bowl is not a 'tabletop wargame', though it is probably closer to other Games Workshop inventions such as Warhammer 40,000 than it is to traditional board games such as Monopoly. Blood Bowl is presently in its third edition.