The smashing, bashing, unstoppable force running down other players is a classic scene in any sport.
The skill Juggernaught brings this to the BloodBowl pitch: A player with this skill is virtually impossible to stop once he is in motion.
This skill is great for two reasons: firstly, it turns a 'both down' result into a push back - which is very handy if your player doesn't have Block as it keeps him on his feet and avoids a turnover. Its other key advantage is that it negates the defensive skills Stand Firm, Fend and Wrestle on the target player. The negative aspect of Juggernaught is that it can only be used as apart of a Blitz action and thus is not good in defence.
Juggernaught is sometimes referred to the poor man's Block skill because its very useful in attack, but not as versatile. However, its generally more accessible to Big Guys (as a Strength skill).