Offensive linemen cannot receive or touch forward throws in virtually all variants of gridiron football, nor can they advance downfield in passing situations. In order to distinguish which receivers are eligible and which are not, football regulations require ineligible receivers to wear a number between 50 and 79. These players are considered non-participants because they do not engage with other players on the field during gameplay.
However, there is an exception to this rule: If a quarterback chooses to throw a forward pass, it can be caught by any player including offensive linemen. This is called a "tackle" catching a pass.
For example, if a quarterback rolls out to his right and throws a forward pass, the only receiver that could catch it is the one wearing number 50.
This exception was created in response to a dangerous play that often ended up killing off momentum for its time. In 1919, the American Football League adopted a set of rules known as "Point-After-Touchdown". Under these rules, if a forward pass was thrown more than 10 yards beyond the line of scrimmage, then it became possible for either team to score by kicking a field goal from where they stood on the sidelines. The reason given for this change was that too many games were being decided by opponents running into each other after long passes had been thrown; this new rule would prevent those kind of game-winning plays.
Six of the offense's eleven players are qualified receivers who can catch a forward throw. The remaining five are ineligible recipients. Once an eligible receiver has caught the ball, the linemen can go downfield to block. Every defensive player is considered an eligible receiver.
A pass is completed when caught by a player or simultaneously by players of Team B, or when such a pass is touched by, or touches B1 and then is caught by B2.
Downfield ineligible player during a throw (5 yards)- Only specific players, including as running backs, wide receivers, and tight ends, are eligible for a pass during a play. A penalty will be assessed if a non-eligible player, often an offensive lineman, is more than two yards downfield on a throw play.
He can't because he's injured - Players are only able to catch passes while healthy. If a player is injured while receiving a pass, he will have to return to the field after being injured.
It's against the rules - Passes cannot be caught by anyone except for the quarterback or a receiver. Catching a pass means either getting your hands on it before any other player does or pulling it in close enough to be touched with both arms or with one arm while in motion.
It's against the rules unless you're a quarterback - Quarterbacks can throw a pass even when they are covered by defenders. This rule exists so that quarterbacks do not always have to rush their passes.
When an ineligible receiver catches a ball, it is generally because the quarterback was under pressure and threw it to an offensive lineman out of desperation. The eligibility criteria only apply to forward passes. A reverse or lateral pass can be lawfully caught by any player.
That said, there are exceptions to every rule. If a quarterback wants his receiver to get open for a catch, he will usually find a way to do so. In fact, many great quarterbacks are known for their ability to put balls in difficult places for their receivers to grab. Here are three famous examples: John Elway, Brett Favre, and Tom Brady.
In conclusion, yes, a quarterback can throw to a lineman if he wants to. Usually, they want to though, because it's what good quarterbacks do.