Does this spell affect creatures above the caster?

Ah, Spirit Guardians. The cleric's version of a breath attack.

In the PHB, this spell requires concentration. It doesn't state it here. I have to keep arguing with players and bring out the PHB over and over to show them. The spell is too strong for it not being a concentration.

Quote from Raul_5 >>

In the PHB, this spell requires concentration. It doesn't state it here. I have to keep arguing with players and bring out the PHB over and over to show them. The spell is too strong for it not being a concentration.

I was wondering bout 'concentration' too.  Is that maybe what the "C" in the black diamond beside the duration represents?  There is no legend ...

Quote from VancouverDave >>

Quote from Raul_5 >>

In the PHB, this spell requires concentration. It doesn't state it here. I have to keep arguing with players and bring out the PHB over and over to show them. The spell is too strong for it not being a concentration.

 

I was wondering bout 'concentration' too.  Is that maybe what the "C" in the black diamond beside the duration represents?  There is no legend ...

 Yes, that's exactly what the "C" means.

That can't be what the C in the black diamond means. I get that C on several of my Paladin spells that are instantaneous. Bless, Divine Favor, Protection from Good & Evil, Thunderous Smite, Shield of Faith...not one says anything about having to concentrate. They are either immediate or 10 min durations. So the C MUST mean something else. 

Although I assumed it meant Concentration and then noticed Concentration was not mentioned in the spell description, I assumed it was meant to mean something else. I thought, after my post, I should have done my due diligence before posting anything on a forum, so I pulled out the PH. It does, in fact, say Concentration on all those spells I listed above. However, since the spell write up in the D&D Beyond DOES NOT say concentration, is it possible, through some errata I am not familiar with, it's changed to simply a duration spell? And they just forgot to remove the C, I've noticed other mistakes on D&D beyond, so forgetting to remove the C from spells that are no longer concentration based, I could understand. 

Anyways, I just wanted to say that after posting that, I did refer to the PH and realized I was mistaken. But maybe not. 

The "C" in the black triangle means that it is indeed a concentration spell.

Just wanted to make that 100% clear if anybody was still confused.

As far as concentration goes...

Normal activity, such as moving and attacking, doesn't interfere with concentration. The following factors can break concentration:

• Casting another spell that requires concentration. You lose concentration on a spell if you cast another spell that requires concentration. You can't concentrate on two spells at once.
• Taking damage. Whenever you take damage while you are concentrating on a spell, you must make a Constitution saving throw to maintain your concentration. The DC equals 10 or half the damage you take, whichever number is higher. If you take damage from multiple sources, such as an arrow and a dragon's breath, you make a separate saving throw for each source of damage.
• Being incapacitated or killed. You lose concentration on a spell if you are incapacitated or if you die.

It does, that's the little C icon before the duration  

Using the Spirit Guardians throw walls?

AoE spells need Los to effect targets,  but  this is conjuration spell , “you call forth spirits” and the damage done to the enemy  is from them.  With Conjuration spells your characters do not do damage, the Items or creatures you summon do the damage for you. And since you summon extra planer “ If you are good or neutral, their spectral form appears angelic or fey (your choice). If you are evil, they appear fiendish.” And most spectral forms move freely throw walls.

This makes the spell one of the most OP of the game.

i cast the spell of spirit guardian and an assasin was hide in the area of the spell.

what happen in this case ??

Unless you knew the assassin was there, and you assigned the assassin as an enemy, then nothing would happen.

You do not need to know the assassin is there. You designate the targets it will not effect, not the ones it will affect. So anyone in the area you dont choose will have to save and be subject to the spell, even if you cant see them

That's true, never mind then.

Can I walk towards an enemy with Spirit Guardians active, putting them into the radius and make them take the damage?

I hope so, because I do this all the time. The spell is centred on the caster and moves as a protective “bubble” around them. 

I'm playing a Divine Soul Sorcerer, so I have access to both Sorcerer and Cleric spells, and I should be reaching level 5 in a week or two. I'm debating whether I want this or Lightning Bolt as my first 3rd level spell. Also, before anyone thinks to suggest fireball over lightning bolt, I sometimes play with someone who uses a wizard and he's going to learn fireball, so I figure I should add variety, and it's a bit of an aesthetic/personality choice for my character.

1. When it says "when the creature enters the area for the first time on a turn or starts its turn there" does that mean, for example, if I use that spell and an affected creature is already in that radius, will it have to make the saving throw and take damage, then on its turn (if it isn't already dead) does it have to make another saving throw and take damage because that is where it started its turn?

2. You're allowed to move and attack (not with another concentration spell) while using a concentration spell, right? So if I move with this spell, will I bring the area with me or will it remain in the original place where I summoned it?

3. Also, when an enemy leaves the area, how is their speed affected? So with half speed, if it's usually 30 and is 15 now, let's say they only need to move 5 ft to leave the area, will they still only have 10 ft left for that turn, or will they have 25 ft?

I'm kind of hoping it doesn't follow me, because then I'd feel like I'd have to chase down my enemies with it, and while it wouldn't be too hard depending on how reduced speed works, I imagine my DMs would immediately just make those enemies turn around and attack me, and since Sorcerer's are glass cannons, if that first enemy hits me and ends my concentration, then the rest of the enemies coming for me would take no damage, so there's no chance they'd die when their turn starts, plus with only the one reaction to use my shield spell, it could only take 2 or 3 good hits to kill me. I'd rather just walk out of the field to get further away from enemies, preferably behind cover so hopefully any enemies with ranged attacks won't hit me and break my concentration, and I can just sling some ranged attacks at them and/or any enemies coming out of and going around the Spirit Guardians to attack me. Learning lightning bolt might come in handy if that limited movement forces the enemies to huddle into positions that are really fortunate for me, and my wizard buddy who has fireball. Just AoE after AoE!

My god, this is what I love about playing D&D, you have so many interesting things to experiment/plan and strategize with, and if you have a good DM, some great opportunities for creative problem solving, some of which should definitely earn you inspiration.

If that's the case, what if another player uses this spell? Do the two of you have to be at least far enough away from each other to not intersect, or an extra 5 ft so enemies can go through the gap? Or can they intersect and will enemies just make one save or have to make a save for each if they're inside that area where they interesect? And what happens if one player's does necrotic damage and the others is radiant?

@drakegaming_twitch This is exactly what the balck diamond C stands for.  All of those Paladin spells you listed are concentration spells as well. Those spells may be instantaneous to cast but you have to maintain you concentration to keep them up. Casters must be pretty OP around your table, lol.