Some of the lyrics didn't seem to fit Littlefoot too well, but as I listened to it, I found that the song did fit enough to make a workable music video. SWHalo2 felt the song could describe Littlefoot's hardships.
New blood joins this earth
And quickly he's subdued
This would describe Littlefoot's birth, and how, in just a few years (not that long of a time in life) he encounters Mr. Threehorn.
The young boy learns their rules
This describes how Littlefoot learns about the dinosaur segregation from both Mr. Threehorn and his mother.
So i dub thee UNFORGIVEN
This is, in my opinion, what Littlefoot would have thought about Sharptooth. In the music video, Sharptooth is the "unforgiven" one due to killing Littlefoot's mother.
They dedicate their lives
To running all of his
This seems to describe Littlefoot's mother and Mr. Threehorn, both wanted Littlefoot to stick to his own kind, whether he agreed to or not. It could also describe Cera's attitude towards Littlefoot a bit.
He tries to please THEM all
This fits how Littlefoot tried to keep his new friends' hopes up that they would find the Great Valley, and tried to be a good leader for them.
He's battled constantly
This could describe how Littlefoot, in a sense, battled through tough times in the Mysterious Beyond, not only physically (with Cera) but emotionally (the loss of his mother).
This fight he cannot win
This could refer to Littlefoot's fight with Cera, and perhaps with Sharptooth as well.
A tired man they see no longer cares
When I see this line, I think of when, after the fight, Littlefoot, too tired to continue the fight, pretty much told Cera to go the wrong way, and indicated that he didn't care what happened to her.
The old man then prepares
To die regretfully
This reminds me of how Littlefoot came back to rescue his friends, and risked his life each time in doing so.
You labeled me
I'll label you
So i dub thee UNFORGIVEN
This could describe how Sharptooth wanted revenge on Littlefoot, and how Littlefoot probably wanted revenge on Sharptooth in return.
This is just my opinion though.