You run up towards him, holding the spear couched near your forearm, and feint a strike towards the face. The sergeant reads a lack of commitment, and sidesteps, dodging the feint. You whip the spear back, and feint a strike to the waist, which he easily deflects off his shield. You back away wearily, giving yourself more space to attack, and suddenly stab at the sergeant's lower leg. The sergeant realizes you're too far away to hit him, and relaxes. You release it at the last second, letting the tiny bit of shaft you were holding back go, and he jumps back at the last moment, stumbling. He quickly recovers, and grounds your spear with his shield, staring into your eyes to make sure you realize the fight is over. Then he smiles, and claps you on the back.
"Well done Elias, well done."
He then turns back to the others, and shouts at them.
"This man here actually knows what he's doing! The spear is a deadly stabbing weapon, but snaking it past a shield or armor can be hard! The most vulnerable targets to hit with a spear are the face, the throat, and the lower leg! A quick, strong thrust to any of those areas can kill or disable a man instantly. At the beginning of the battle, you feint, just like he did. Small, uncommitted attacks, probing your enemies defense and looking for weak points. Now, for the next part. Elias, prepare yourself."
He gestures to your shield, and casually raises his sword.
((The fight rolls were pretty close at the end. You got a bonus because of your intelligence and Andres' idea, and he got a big bonus because he's...an actual soldier.