It's been a week now, and spike is having dreams about the everfree forest. When he wakes up, his head hurts extremely. Twilight and Fluttershy were the only ones that could tell there was something wrong with him. After explaining to the other ponies what they think, he denied it, and refused help.
Finally, he had to shut them up, and go get some coffee. He jumped at Fluttershy, and tried to strangle her. When Rainbow and Twilight got him off, a party of guards came in. Then they all bucked him several times. There were cuts and marks in Fluttershy's neck, and blood where spike had fallen.
The guards took him to the arena, where criminals fight to the death. Spike was in for a week, and wasn't disturbed that he survived that long. To him, it was like practice for his six "friends" in Ponyville. "I will get out, and you all will die for getting me in here," he thought. "There is no running. Only fighting me and trying to survive it."
Finally, he realized, "I know what I did wrong. I jumped into it blindly! I need an organized plan to escape, and silently kill them." So, his plan was to call a guard, and then bang his head on the cell doors. As the guard is knocked out, he would take the key. He picked up the guard's spear, and fought his way out. It all went as planned.
It sucked. I'm not being a troll, but you have a lot of issues with this story. Please answer these in the story: Why is Spike getting headaches? Why does he want to kill the mane six so badly? Can't he deal with the headaches? How did the guards come so quickly?
Another point you need to address: Gore. It isn't worth it if you have a story with a gore tag, but there is barely any blood. Ya' have to lengthen up the descriptions, let us feel what is happening.
Why is Spike in an arena? Wouldn't there be a trial? How are the mane six's reactions to this terrible tragedy? Couldn't they stop Spike?
Describe the arena. What was it like? Who was there? How did he get ahold of a guard's spear so quickly? How did he fight his way out?
Other than that, you are off to a good start.