One of the smallest games in the Blue & Gray series, First Bull Run only appears in the Decision Games edition. It shares the same map as the Second Bull Run game in the same box, although it doesn't bear much resemblance to the later fight.
The game follows all the usual rules for B&G.
There are just a couple of special rules. The most important being that the Confederate units can't move during the first two turns unless Union units cross Bull Run. There's a similar rule preventing Runyon's Division, a 10-factor Federal unit, from moving unless released by the Confederates crossing Bull Run.
Both armies are very small.
The Federal force comprises 11 infantry brigades with a total of 74 combat factors. There's also Runyon's 10-factor "division" garrisoning Centerville but it only enters play if the CSA crosses Bull Run. Considering the Rebels have no reason to cross said waterway that unit almost never plays a role in the game.
The Confederate forces are considerably more diverse. There are a dozen infantry brigades ranging in strength from 2 to 8, a pair of one-factor cavalry units and a pair of artillery units with combat strengths of 1 and 2. The total CSA force adds up to 77 factors, so the two sides are very evenly matched.
Victory comes from routing the enemy army. At the end of every game turn each player rolls a die. If the die roll is 17 or higher then his army routs. There's a +1 die roll modifier for every ineffective unit and a +2 for each eliminated unit.If neither side routs by the end of turn 8 then geographical objectives come into play. There are two, Groveton and New Market. Control of both is needed to win.
There are two ways for the battle to end in a draw. If neither army routs and each controls one objective, it's a draw. If both armies rout in the same turn, it is also a draw.
The general edge in the game goes to the Union side, according to results on the Hexwar.com wargaming site, which show 770 U.S. wins, 439 C.S. wins and 308 draws as of Jan. 22, 2008.
While the Federal side doesn't have a strength advantage, it does have the initiative from the start of the game and a more compact striking force. Typically the initial Federal attack will destroy the 2-factor infantry and artillery units guarding Stone Bridge, putting them up +4 in the contest to force a rout. Still, the Union player as to be careful because one set of bad rolls can easily render a large part of his army ineffective. Besides adding to the rout probability, this will often gut any further offensive potential for the Federals.
The Confederates have some trouble forcing a win, however, unless they can entice the Federals into pushing their offensive too far. It's fairly easy for the Federal player to settle for a draw if they end up with a large number of ineffective units. Groveton is not too hard to defend in the limited time available for a CSA counteroffensive and there's a real possibility such a counterattack could end up handing the Union player a victory after all through adverse combat results against the Rebels.
Still, it's a quick-playing contest so the scenario can be played several times in a single session.