Rules:
Movement
Infantry have set movement, depending on their type.
Light Infantry have a Walk of 1, a Run of 2, and a Sprint of 3.
Medium Infantry have a Run of 1, and a Sprint of 2. Medium Jump Infantry can Jump up to 5 hexes (max 16 hexes)
Heavy Infantry have a Sprint of 1. Heavy Jump Infantry can Jump up to 3 hexes (max 16 hexes)
Motorized infantry have a cruise of 5, and flank of 8, using personal wheeled vehicles.
Foot Movement: Infantry may move in any direction when using ground foot movement (not jump or wheeled). Jump movement follows normal Jump movement rules. Further, infantry have no facing (although some specific weapons still must set a facing before firing). Infantry do NOT ignore the movement modifiers to shooting or MP costs for terrain. If entering terrain requires more MP then the Infantry have, they may always use the minimum movement rule to move 1 hex each turn, but can never shoot when using the minimum movement rule.
Sprint: An infantry that uses Sprint MP may not shoot.
Jump: Jump infantry, unlike their more advanced Battlearmor cousins, only have 16 total Jump MP each scenario due to limited fuel, after which the Infantry can only use their ground MP.
Motorized movement follow all movement rules for wheeled vehicles, including having a facing and paying for turns like a wheeled vehicle. If a Piloting Skill roll would be required, use the Driver's Gunnery skill instead. On any failed Piloting Skill roll, the Infantry are forced to Disembark immediately in the hex where the failure happened, and can not shoot that turn. They are then treated as foot infantry for the rest of the battle, of the light/medium/heavy type as normal. Motorized infantry can also voluntarily leave their Motorized vehicles at the start of any movement phase, but can not re-embark for the remainder of the battle.
Shooting
Infantry have no facing in most circumstances (see weapons with crew for the exception), so can fire in any direction, including when Motorized in personal wheeled vehicles. Infantry take all normal penalties for walking/cruising, running/flanking, and jumping.
Infantry weapons have many restrictions based on moving and shooting in the same turn, often due to needing to reload after each shot, or setup and tear down before shooting or moving. Except for Crewed weapons, which require multiple troopers to fire one weapon, each trooper may fire one weapon at a target of their choice in the shooting phase. Infantry squads take secondary targets penalties as normal.
Crewed Weapons: If a weapon specifies a crew number, it can only be operated in teams with enough troopers to equal the crew value. It takes all crew troopers shooting to fire the crewed weapon—the troopers acting as crew can shoot no other weapon the turn they shoot a crewed weapon OR move with a crewed weapon (they are too busy packing up the weapon on a turn they move to do any other shooting!), and the weapon must remain stationary to fire. On the first turn the crew is stationary, they must set a firing facing for their weapon. They may then shoot the Crewed weapons one time in the shooting phase. On subsequent turns, if they remain stationary they can either set a new firing facing in the movement phase and fire one time, or keep the facing from the previous turn, and fire the Crewed weapon twice. If the crewed weapon is noted with 'Loading', specifically Mortars and AA weapons, then it takes two shooting actions to fire the weapon, the first to load the weapon and the second to shoot. This means Mortars/AA weapons can only fire after remaining stationary for 2 turns, and only if they do not change their facing on the second/subsequent turn. A team may abandon their crewed weapon at the start of their movement phase—mark the weapon as destroyed. The team can then move and shoot as normal, no longer burdened carrying the support weapons. The weapon is automatically destroyed in this way when the troopers in a team fall below the crew value for the weapon due to casualties.
Small Arms. All Small Arms carried by infantry have large penalties to hit, representing the difficulty of causing damage with small rifle weapons. However, if the infantry remains stationary they receive a -1 bonus to hit that turn with Small Arms attacks, as they are able to take a more careful aim.
Walking Fire. Some weapons have a low ammo count, and must be reloaded often, but not so often that the weapon must remain stationary—the classic example is the 2 shot SRM launchers. These weapons can only be fired when Stationary or Walking—they can not be loaded and fired in the midst of running across the battlefield.
Stationary Fire. Some weapons require the full attention of the operator to load and fire each turn, such as with the Recoilless Rifle which has a dangerous back blast and requires extra care when shooting. Weapons with the Stationary Fire notation can only be fired when stationary.
One Shot. Many Infantry weapons are noted as One Shot, or OS. From Disposable LAW/Light Anti-armor Weapons, to Grenades and Satchel Charges, after they are used they are crossed off the record sheet and can no longer be used.
Motorized Vehicles and Shooting: Motorized Squads have the same fire restrictions as Foot infantry, replacing Walk for Cruise and Run for Flank. If a crewed weapon is part of a Motorized Squad, then the facing that is set is one of the Vehicle Firing Arcs. The crew must still remain stationary to shoot a crewed weapon—despite being mounted on the personal wheeled vehicle, the Motorized vehicle has no fire control or stabilizers found on traditional combat vehicles that allow accurate enough shooting while on the move. For vehicles with hull mounted weapons that can shoot on the move, instead of infantry shooting from the back of an open top, use the support vehicle rules.
Spotting. To spot with infantry, a trooper must use the 'Communications' gear as a weapon attack. This means a trooper may not spot and fire a weapon, though other members of the squad can shoot as normal. Spotting counts as the primary target—this also means each infantry squad can only make one spotting action each weapon attack phase even if multiple teams have Communications gear. All normal spotting modifiers apply, including 'spotting unit made attack this turn' modifiers.
Taking Damage
When shooting at infantry, all non-infantry units must take a +2 penalty when shooting Foot/Jump infantry due to their small size. Battlearmor and Motorized Infantry instead take a +1 penalty when shooting at Foot and Jump infantry.
When infantry squads take damage, the damage must be randomized among the different teams. Roll randomly to determine the team hit by each weapon, exactly the same as Battlearmor troopers in a squad.
When a weapon specifies it does extra damage to infantry, such as a machine gun with 2d6 damage versus infantry, roll location and then apply the modified damage. For example, an LRM20 with fragmentation ammo rolls a 7 for cluster, dealing 12 damage in 5 clusters. After rolling which team is hit by the 5, 5, and 2 damage clusters, the team would take double damage for fragmentation missiles, taking 10, 10, and 4 damage.
Infantry do not suffer critical hit effects, but when a team takes damage but is not destroyed in a turn, in the next turn one trooper in the team can not fire, and the entire squad can not sprint or take any other action that would prevent them from shooting. After this trooper skips their shooting when the squad is activated to fire, the team has recovered, and can act normal (barring any new damage). It is thus possible, with a large cluster attack, to pin heavy infantry (who can only sprint, which is disallowed after taking damage) in place, until the squad is either destroyed or stops taking damage.
Example: A standard infantry squad get hit by an SRM4. Three missiles hit, destroying team 4 and damaging but not destroying team 2 and 3. In the next turn, because the squad took damage but the damaged teams were not destroyed, team 2 and 3 may not shoot with one trooper each (if they have only 1 trooper left, the team may not fire), and the entire squad may not sprint. After not shooting with team 2 and 3, they may act as normal the following turn.
Motorized infantry: Motorized infantry all have one driver acting as an individual, and passengers activating as a second team in the same vehicle. The Driver of each Motorized vehicle gets one extra point of armor representing the Barrier effect of the vehicle, which is lost if the squad dismounts. While still Motorized, the driver can not shoot any of their weapons, but once dismounted the driver team may then shoot as normal. If any driver team of any vehicle in the squad is destroyed, with passenger teams still alive, then the Squad must remain stationary until either the Passenger teams without a living Driver team are also destroyed, or the entire squad dismounts.
Anti-mech Attacks and other Close Assault (range 0) attacks
Antimech equipped infantry types can, when in the same hex as a mech or vehicle, execute Swarm or Leg Attacks by attacking with Grapplerods or Satchel Charges. Each trooper must make the same attack that turn, and be capable of attacking (so a damaged squad that has not recovered can not make an Anti-mech attack). The modifiers for Anti-mech attacks are the same as battle armor, treating the Teams as the number of Battlearmor members active. Unlike Battlearmor, Swarm and Leg attacks for infantry are each One Shot, though a team may carry multiple Grapplerods or Satchel charges per trooper to attack more then once.
When attacking at Range 0 but not making an Antimech attack, infantry are said to be in Close Assault. Unlike other units, who may not make shooting attacks at range 0, Infantry can still shoot at range 0, but with a +2 penalty. Some weapons have a range of 0 listed. These weapons, such as Grenades and Vibroblades, are designed for close assault and do not take the +2 penalty when used at range 0.
