Offensive linemen in football hold hands in order to have a good idea of the gaps between the players, and to correctly position themselves in different formations and setting off with the correct timing on ball throws without losing orientation. The tactic also helps bring consistency to the line formation every time. At the same time, the tactic also helps offensive linemen get a good idea about the time when the center snaps the ball, avoiding a false start due to the faulty sense of timing. This is sometimes the case when offensive linemen are unable to hear the quarter back due to the noise in the arena.
However, it is important to mention that while it is legal for linesmen to hold hands for a certain time and distance, they are not allowed in any way to hold the defensive tackle linesmen, or obstruct them with an extended arm. This is considered a serious offense and can result in a 10 yard penalty from the line of scrimmage.
The duties of the offensive linemen vary according to whether they are rank or interior linemen. The primary duties of the linemen are to create spaces for the effective forward movement and also to prevent the opposite defensive line to resist that forward movement by slowing them down. There are strict limitations to the movement of interior linemen and to how much they can manipulate, so they try making the most of their space by tactics such as holding hands to calibrate spacing.
Some people also think that linesmen holding hands can sometimes be reflective of team unity and solidarity. While there is nothing to disprove this notion, it has little to do with any value it holds in terms of field tactics.
While this field tactic is useful, it is not a frequent sight in professional football games.