During the first round of combat between the Black Knight and a pair of Heavy Trolls, the Black Knight failed to strike Troll 1. Fortunately, the two Heavy Trolls also missed the Black Knight.
So now we move to the second round of combat, above. Troll 1 is once again the target of the Black Knight, and is placed, initially, in pink attack box 1, with Troll 2 placed in box 2.
Because the Black Knight missed during the first combat round, his mace becomes "alerted" (flipped over from its white to red side). When alerted, the Black Knight's mace has a speed 3 regardless of the Black Knight's Fight chit speed, and the mace is faster than the Trolls' move times of 4. That means we are guaranteed to score a kill, no matter what maneuver the Troll attempts, as we will undercut the Troll's maneuver.
Again, the shield is placed in the Thrust box, to cover the Black Knight's H4** Charge maneuver. The H4** move is played, as we want to avoid the attack of the second Troll, if possible.
During the combat resolution phase, Troll 1 once again repositions to the bottom-most smash and duck attack box. However, even though the Black Knight fails to line up with the Troll 1, the Black Knight's mace attack speed of 3 is faster than the Troll's maneuver of 4, so the Black Knight hits him. Because the Black Knight used a Heavy Fight chit, the mace does heavy, rather than medium damage, thus killing the Troll (the red X through Troll 1 denotes a kill).
Troll 2 failed to line up with the Black Knight's Charge maneuver, as he was anticipating that the Black Knight would try to Dodge, and the Troll's M4 attack was not faster than the Black Knight's H4** maneuver, therefore the Troll did not undercut the Black Knight.
As a result of the Black Knight's double effort star (**) maneuver, he suffers additional fatigue, so he will have to put aside a second chit. Now the Black Knight will have to spend two "Rest" phases to recover the chits fatigued during the combat with these Trolls.