Rest API can only get the teams in Team Project for now, it does not support create teams. Refer to this link for details: Teams. You can submit a feature request on VSTS User Voice.
The alternative way to achieve this is using .NET client libraries for Visual Studio Team Services (and TFS), following is the code sample:
using System;
using System.Collections.Generic;
using Microsoft.TeamFoundation.Client;
namespace ConsoleApplica
{
class Program
{
static void Main(string[] args)
{
string URL = "https://xxxxxx.visualstudio.com/";
TfsTeamProjectCollection ttpc = new TfsTeamProjectCollection(new Uri(URL));
TfsTeamService tts = ttpc.GetService<TfsTeamService>();
string teamprojecturi = "teamprojecturi";
string newteamname = "newteam";
string teamdescription = "newteamdescription";
IDictionary<string, object> prop = null;//properties, can be null or empty
tts.CreateTeam(teamprojecturi, newteamname,teamdescription,prop);
}
}
}