The support role has 3 main jobs in Smite, each of which vary in importance as the game progresses into the later stages. It should be noted that since Season 2, the Support role is now the most difficult role to play well.
First and foremost, the Support is required to protect the very weak Hunter in the Long/Duo lane at the start of the match. This is done by having the ability to peel (which means to stop enemies attacking the Hunter) using Crowd Control abilities and your own natural tankiness in order to take damage that would otherwise be killing the Hunter. As such, one of the most important aspects of any Support character should be their Crowd Control and their health/defense capabilties.
Around 3 minutes in, the Mid Harpy camps will spawn, which offer a large amount of XP to the God(s) that kill them. These are meant to be contested by the Support on the Duo side, and in order to guarantee a kill you will almost certainly need the time and space to deal enough damage. This requires zoning in order to keep your rival Support God away from the camp long enough to secure the camp - which again relies on CC abilities, as well as being able to deal and take damage effectively. In the mid to late game, the Support will find themselves under-levelled unless they frequently take Harpy Camps, so this is very important.
Finally, the Support must be able to rotate from lane to lane quickly when needed, and must have presence in a team fight (by which I mean must be able to initiate a large battle). As such, Supports with good mobility and peel excel here, such as Athena (whose Ultimate ability allows her to teleport to any friendly God, and who has an ability that draws enemies to attack her rather than team mates).
In short, Supports require;
- Good Crowd Control
- Good mobility
- An ability to take a beating
This three aspects are the most important things that a Support character needs.