Horsemanship
From MTG Salvation Wiki
Horsemanship is a keyword ability on creatures that serves as an evasion ability. Attacking creatures with horsemanship can not be blocked by creatures without horsemanship. It is functionally identical to flying, however a creature with only one ability cannot block a creature with the other ability.
All cards with horsemanship appear in Portal Three Kingdoms. Until the set was made legal for Vintage and Legacy in October 2005, it had the distinction of being the only keyword ability existing outside of Un-sets that did not appear on a single card legal in any tournament format.
From the Comprehensive Rules
|

