Lee Sin is a Ranged, Melee, Tanky, DPS, Assassin, Mage, Suppport, Jungler. His wide spectrum of abilities and build paths allows him to be one of, if not, the most unique and varied champion in League of Legends. This build will is about the not very popular support side of Lee Sin ;].

This build is all about helping your allies to stay alive and do more damage to your enemies. Mostly by just jumping at the enemy slowing it(Insec), jumping back to your adc (buffing it) and let him kill it.
This is not a troll build, but also not a pro build to win your ranked games.

Pros:
- Good Shield.
- Good survivability / Lane sustain.
- Displacement ultimate.
- Unpredictable.
- High mobility.
- Fun to play

Cons
- Hard to learn.
- Useless if not played well.
- Ultimate may safe an enemy.
- Needs nice teammates.

Sonic Wave/ Resonating Strike
The first part of this ability fires a line skillshot. if a target is struck they are revealed and resonating strike becomes active. With a target marked Lee Sin can activate Sonic Wave / Resonating Strike again to jump at the target dealing more damage the lower the targets health. This can be used offensively and defensively. Throwing Sonic Wave / Resonating Strike at a jungle camp and then activating its second effect to effectively gain a free flash. Max this last.
Jump to enemies and use E slow them to help your team escape or kill enemies.
Safeguard/ Iron Will
The first half of this ability shields Lee Sin and a friendly target while Lee Sin dashes to the target. The second half gives lee sin life steal and spell vamp.
Max. this skill first for support Lee. It is a very strong shield takes up to 240 damage every 3 seconds on 1 friendly champion later in the game. (with Abdent Censer unlimited +25% Attack Speed for one teammate!).
Tempest/ Cripple
The first part of this ability deals damage in an AoE and reveals targets. The second part slows all affected targets and reveals them for longer. This helps your teammates escaping enemies and killing enemies. You can jump back to your allies after using it to safe them or u can use your ultimate to kick the enemy in your team.
Dragons Rage
This is Lee Sin's ultimate ability. Lee sin roundhouse kicks a target dealing damage. The kick knocks the target back and anyone hit by the target is knocked up for a duration. If a target is hit against terrain they are effectively stunned for the duration of the knock back. Good to help your teammates kill and escape.

Combination of these skills makes Lee Sin a good support. That is hard to pin down. He has good CC, knockback and shield to escape- and help teammates stay alive.