Tag.java

public class Tag {

      private final Scoreboard scoreboard = new Scoreboard(); //you can use one for the nametag, no need to create other

      public ScoreboardTeam getOrCreateNewTeam(String name) {
        final ScoreboardTeam team = scoreboard.getTeam(name);
        return team != null
          ? team
          : scoreboard.createTeam(name);
      }

      public void updateNmsPlayerTag(Player player) {
        String name = player.getName();
        name = name.length() > 15
          ? name.substring(0, 15)
          : name;

        final ScoreboardTeam scoreboardTeam = getOrCreateNewTeam(
          String.format("%s%s",
            "a", //the priority on the tablist, "a" = 0, "b" = 1 bla bla bla
            name
          )
        );

        scoreboardTeam.setPrefix(getSafetyName("Tag do time"));

        scoreboardTeam.setSuffix(getSafetyName("suffix do time"));

        final Collection<String> playerNameSet = scoreboardTeam.getPlayerNameSet();
        if(!playerNameSet.contains(player.getName())) {
            playerNameSet.add(player.getName()); //ADD PLAYER TO SCOREBOARD TEAM
        }

        PacketAccessor.sendToAllPacket(
          new PacketPlayOutScoreboardTeam(scoreboardTeam, 1), //REMOVE EXISTS TEAM
          new PacketPlayOutScoreboardTeam(scoreboardTeam, 0) //CREATE NEW TEAM
        );
    }

     public String getSafetyName(String name) {
        return name.length() > 16
          ? name.substring(0, 16)
          : name;
    }
}

all classes come from net.minecraft.server package, be carefull with imports!