Support
Overview
Role
Offensive
ECM (Electronic Counter Measures): ECM modules allow you to jam an opposing ship, breaking its lock and making it unable to lock anything else for 20 seconds. Being able to stop a enemy ship from targeting is always useful. It can be used to jam the opposing fleet's logistic ships, preventing them from repping their fleetmates while you massacre them, or used to save someone from being tackled by jamming the tackling ships, or just stopping enemy damage.
Tracking Disruption: Reduces the tracking speed (ability to hit moving targets) and optimal range of the turrets on the enemy ships. Generally they should be used on large battleships which have trouble hitting smaller targets. Unfortunately, this will not affect missile users at all. It has a niche useage in large fleet fights. But if used correctly, can be very effective.
Sensor Dampening: Sensor Dampeners reduce the lock range and/or scan resolution (locking speed) of the targeted ship. Unlike ECM, this has a 100% chance of affecting the targeted ship. Damps almost always use scripts and the script most commonly used is the lock range dampening. Only useful on a ship with bonuses to it and only really useful in small gangs. The major drawback to damps is unlike ECM where 1 mods can successfully lock out a target, it normally requires 2-3 damps to successfully lock one out.
Target Painting: Increases the signature radius of the targeted ship, making it able to be locked faster, and easier to hit.
Defensive
Remote Shield/Armor Repairers: Repairs the target ship's armor/shields.
Logistics ships are specifically designed for this role.
(Remote) Sensor Boosting: Boosts the target ship's Scan Resolution, thereby reducing locking time. Good for gate camping and for logistics ships.
Tracking Links: Boosts the target ship, giving it a higher tracking speed and optimal gun range. This does not affect missiles.
Fleet Booster: Increases various abilities of all subordinate ships. Most effective on a Command Ship and matching Mindlink implant.
Guides
There are many ways to perform the Support role in fleet. This role generally does not receive praise, or appear on killmails but all fleet fights would be lost without them. These are the unspoken heroes, the watchful guardians, the silent protectors. You're basically Batman.