Fighting the Lancer

The Lancer or the Sixth Ranger has a disagreement with the hero. It could be philosophical or it could just be for the hell of it. This can be anywhere from tension to a refusal to fight to a downright Face Heel Turn. The closest thing to The Starscream to happen to the good guys.

Examples of Fighting the Lancer include:

Anime & Manga

Yamato (Matt) does this to Taichi (Tai) in the first season of Digimon.
Hilariously done in One Piece. After being treated to drugged food by a bunch of bounty hunters, Zoro the lancer beats the ever-loving crap out of them. Luffy wakes up, and thinks that Zoro just attacked the people who were nice to him and gave him food; a battle ensues.
- Played much more seriously latter in the Water 7 Arc. With a growing conflict between Luffy and Usopp, due to emotional problems Usopp started developing during the arc, and Luffy's decision regarding their ship (which Usopp was very fond of); the conflict grows into fight between them.
Naruto built up to his confrontation with Sasuke for the entire first part of the series. Their first pre- Face Heel Turn fight was a stricter fighting the lancer, but their second was the final and most intense battle in the entire child arc.

In a way, Xavier did this to Magneto.
Wolverine and Cyclops have a fight (and subsequent split) in Schism.
- They have had plenty of fights and arguments before then.
The fight between Hal Jordan and Guy Gardner to see who would be earth's Green Lantern. John Stewart was committed to Oa at the time.

Padmé and Obi-Wan do this to Anakin in the Star Wars prequels.
Cera to Littlefoot in The Land Before Time.
While Leonardo and Raphael have no small history of arguments, this was arguably the main plot of the fourth movie TMNT.
Jayne and Mal in Serenity, an argument starts, and Hilarity Ensues
Tony Stark and Steve Rogers have the most friction of any of the Avengers, and their most heated argument almost turns into a full on fight before it's interrupted.

The Star Wars Expanded Universe has Legacy of the Force, where just about everyone does this:
- Han doesn't like that Luke puts Jacen and Jaina in danger, after what happened to Anakin...
- Everyone abandons Jacen Solo.
This happens in the seventh Harry Potter book, when Ron leaves Harry and Hermione after getting into a fight with Harry in the woods

The 2011 adaption of Thundercats is famous for the little... scuffle between Lion-O and Tygra. But the original Lion-O and Tygra also came to blows a few times.
In Xiaolin Showdown Raimundo, the lancer of the group, is often at odds with the other members and even Master Fung. At one point, he flat out disobeys direct orders from the latter and betrays Omi and his old master after being reprimanded, and turns to the opposing side for a brief period