Cowboys' Zack Martin skips team flight, holds out from training camp over contract dispute

Zack Martin did not travel with the team to training camp, wanting his contract addressed.
Martin believes he is underpaid compared to other top NFL guards.
Martin could be fined over $900,000 if he skips camp entirely.
The Cowboys rely heavily on Martin's performance for their rushing offense.
Martin hopes to get a new deal similar to the league's highest-paid guards.