We tend to forget about it, but Valorant is only in beta test, which means we shouldn't be surprised about the fact that there are only three maps contained in the pool.
Just as Bind or Haven are each distinguished by specific graphic characteristics and mechanisms, Split is a very different map from its two counterparts.
Thanks to its very advanced mid — that gives access to both sites via overlooking positions — Split can be held pretty easily by controlling three different points.
The map is also the only one to contain ropes, a tool that you can use at your advantage with the proper technic.
In defense
Split is the most closed map in defense with three main choke points against four for Haven and five for Bind.
Initial Positions
A Main is difficult to hold correctly without attacking the area. Most of the time, one static player will defend the point by positioning in A Ramp/A Heaven — or even Screens if you get your hands on an Operator. He will certainly need the help of a pivot player in A Ramp/Heavy ready to rotate mid by using ropes.
The B Site requires two static players to defend it, one positioned in Back B or on the site itself, and the other in B Heaven/B Stairs. The last player will be rotating from A to B, depending on the current information on the enemy team.
Defend mid
In case of aggression via Bottom Mid/Top Mid, the mid player can fold back and prevent flanking on A by covering Mid Vent or fall back in Mid Mail to try to pick a kill.
Defend the B site
In case of aggression on the B Site, the static player covering B must play for time, waiting for the support from the pivot player positioned in B Heaven. The pivot player located in Top Mid or Mid Vent needs to rotate in Mid Mail to cover from a potential flanking.
If the first defender is cornered, Back B can be a very good fallback solution to delay in close combat and not leave a fallback point for attackers until support comes from B Rafters and B Heaven.
Defend the A site
Most aggressions on A are theoretically easier to defend against, but everything can become pretty tricky if the opposing team manages to take control of A Heaven. At this point, they will be able to crossfire the site, from A Main and A Rafters.
Two players will be needed to cover A Ramp and Mid Vent, depending on the information acquired on the opposing team, meaning the pivot player located in Mid Vent should take the ropes and come back on the A Heaven side to cover them.
In case of an A rush situation, the static player located in A can rotate to Screens or Elbow to play for time while keeping an ear on a possible planting.
Attack
As always, there are two main possibilities: taking positions, lines, information, and play slowly or rush directly to the site by using smokes, flashes and other grenades.
The importance of mid
Don't hesitate to use equipment in Bottom Mid / Top Mid to force the opposing pivot player to stay there or to create openings if you manage to take down one opponent.
A good ear positioned near the Bottom Mid box will normally identify enemy pivots if your team tries to attack the extremities. Do not hesitate to move the enemy defense by feigning rushes, as holding the Bottom Mid also opens the possibility of rotating in A Sewer.
Always keep in mind that taking down a pivot player isolates his static player and encourages the rest of his team to reposition themselves to fill the spaces.
A Top Mid / Mid Mail incursion offers decisive access to B via Heaven or to A via Mid Vent.
Taking positions in B Stairs and A Heaven will be a very important element to prevent the defenders from rotating.
TL;DR
Split is very closed with only three main choke points, but the slightest kill will force the defenders to adopt a very static position while isolating its members.
Mid is definitely the most important axis as it will allow you to put great pressure on your opponents, whereas you're in defense or attack.
