Lineorcs (or linemen as some insist on calling them) are not heavily used in most Orc teams. A maxed out team will have 4 blitzers, 4 black orcs, 2 throwers and a troll. Then there are a couple of spots for reserves filled with Line orcs and goblins. Traditional starting line ups may even only contain a couple of line orcs too.
Line orcs stack up well against many other teams' line men. MA5 isn't ideal - but its faster than zombies or Dwarf blockers. Average strength and agility mean they can block and handle the ball a bit. Armour 9 is a big bonus. Compared to say a human lineman having the extra point of armour makes them much better at soaking up punishment and letting the rest of the team win the game.
However line orcs are worse than the positionals in the Orc team so don't get much play time. Only having General access means that their development potential is worse than the other orcs. Black Orcs are stronger and that makes them much better in the blocker role. Blitzers are faster, start with Block and have strength access - all for only 30k more than a line orc. Goblins give options not otherwise available to the team. Compared to a thrower they don't look so bad +Av vs Pass, Sure Hands and passing access for 20k. So some coaches in short leagues and tournaments, where throwers are less likely to develop, think they represent better value for the team. Where you are allowed to "buy" skills a Line orc with leader is still cheaper than the equivalent thrower. The other side of line orcs is that they are less efficient in TV terms than most other players. A +MA Block lineorc is 20k more TV than a rookie blitzer, and has less potential for development.
So generally the only reason to have line orcs on the team is early on when you can't afford the full team, and then as a alternative to fielding throwers - particuarly on defence. So a common pattern is for an orc team to have two throwers built for offence and two line orcs built for defence. So when kicking the line orcs get fielding, when receiving the throwers. That of course assumes you've got the troll and all the BOBs and Blitzers. If any of those aren't available for any reason then you are more likely to field some more line orcs.
Block or Wrestle
One of the key questions is what skills to give line orcs should they be lucky enough to skill up. My general view is that giving them Block or Wrestle first is crucial for them to get to a 2nd skill. Skills like Kick or Dirty Player, which are useful to the team, don't help them gain SPPs and may even reduce the already limited game time they'll get. Even if you do take a specialist skill first then you'll probably want Block or Wrestle second.
Prior to LRB5 Block was the automatic first choice. It significantly increases reliability when blocking and increases the chance they'll stay on their feet when hit. Single dice blocks are less of a gamble too.
However Wrestle, introduced in LRB5 provides some interesting options that aren't available otherwise. Wrestle enables the player to make both players go prone on a both down result - regardless of whether your opponent has Block. That can be very useful for hitting ball carriers with block or blodgers. Defensively it can be annoying for an opponent to be placed prone if they get a both down result. I think a little bit of Wrestle is good for a lot of teams as it helps deal with teams loaded with Block as well as Blodgers when you are light on tackle.
For me the crucial reason to favour Wrestle over Block on line orcs is that you aren't likely to take it on anyone else (or at least not early on). Blitzers start with Block, adding wrestle, although useful isn't in my opinion as effective as the other options (tackle, mighty blow, guard etc). Trolls and Black Orcs are relatively slow and often built with guard - so want to stay on their feet as much as possible. Throwers are often all ball carriers and therefore don't want to go prone much. So that sort of means if you want Wrestle on the team - which I do - then line orcs is the best place for it to go.
One of the obviously specialisations an Orc team wants but can find difficult to accommodate is that of a Kick player. Kick is a very useful team skill and can really help set the tone of the offence. This is particularly true on table top where you can chose the location of the kick. On the Orc team the obvious candidates for Kick are either a defensively built thrower or a line orc. The downside of Kick on a line orc is that to use the skill you can't be on the LOS or in a widezone. These are places that line orcs often get set up so my slight preference is for Kick on a thrower.
The other team specialist role is fouler. A line orc with Dirty Player is an obvious way of adding this specialist to the team. There are a couple of downsides. First of all foulers are generally better fielded on offence when you've got a better chance of controlling play and building up fouls with numerous assists. Secondly fouling is a lot less effective since LRB5. That means the whole idea of having a specialist fouler is something you'll need to think about. If you want to foul then you really need the skills to make it work. Now a Sneaky Git/Dirty Player is a powerful fouling tool that can be used to great effect. The massive advantage of the SG/DP combo is that you can foul fairly indiscriminately - without having to get lots of assists - safe in the knowledge that if you are sent off you've got better than a 50/50 chance of having your opponent off the field too.
If you do want to foul I'd recommend a slightly larger roster than might otherwise be the case.
With the exception of Sneaky Git, described above, there are two very good candidates for doubles. Guard is a favourite for many Orc coaches. Extra guard is always good and it helps reduce the need for it on other positions even if you want to restrict yourself to four or five. Dodge is another common option. Orcs don't have it normally available. For me the problem with taking dodge is that most teams will have a couple of tacklers. That means if you have a small amount of dodge then you are likely to attract the tacklers, negating the skill. So either take no dodge at all (or just on throwers) or take it on pretty much every double you get so that you've got so much you can overwhelm the number of tacklers on most teams.
Other options that are interesting are Diving Tackle - great for helping pin players down and good in combination with Tackle and Wrestle too. Leader is worth a mention - 30k in TV instead of 60k for a team reroll. Its good value especially early on when you might need the reroll more. However none of these doubles help the line orc develop that 2nd skill and so you need to take that into account.
+ST is a no brainer. Sure it makes him a 100k player but 5439 is an impressive stat line and Orc teams with a couple of +ST are almost untouchable by other bash teams and very hard to break down defensively. I'd be force feeding him touchdowns until he got 16 SPPs and Block.
+AG is also too good to pass up. It isn't as good as on a thrower, blitzer or goblin but extra AG helps in many tight situations.
6,4 is interesting. +Av reinforces the toughness - but doesn't help with development. Also it doesn't help against Claw. I prefer +MA since speed is an area Orc teams are lacking and another MA6 player can make a big difference.
On a 5,5 I'd normally take the double since I think they generally offer further development.
Second or third skills on Line Orcs without a stat or double start to become sub-optimal. General only access makes Tackle (after Block or Wrestle) the stand out skill. I'd be aiming for about four tackle on a mature Orc team so freeing blitzers from taking it is good. The combo with Wrestle is particularly good for taking down blodgers. After Tackle the options really start to thin out. Shadowing is almost pointless on a MA5 player, Pass Block useful against passing teams, but useless otherwise. Pro handy, but there aren't too many rolls you'll make that aren't going to be turnovers so you might end up wasting it.
This brings up an interesting question. For those who are particularly concerned about keeping TV low are skilled line orcs worth having at all? Compared to the other members of the team they are expensive. So there is a line of though that says if you get to 31 SPPs then retire them in favour of a rookie and knock 60k off your TV. I don't subscribe to that view myself and I'm happy with "fatter" teams as I feel they do better during the lean times.
Line Orcs aren't a particularly vital component of most teams. Either filling in on defence or just being spares should some of the more valuable players be unavailable (MNGs even happen to Orcs...). They can be useful specialists too. Get lucky in development and they can have a bigger impact. So largely they are the supporting cast. They can be useful, particularly when built to fill the niches the rest of the team don't want to. Many coaches will develop them a little bit, but then let them stagnate. Two or three skills is the most they need and if they get much more developed they can unnecessarily bloat your TV.