Flutter/Dart Json Parsing

You can copy paste run full code blow
You can return List<TeamDetail>
code snippet

Payload payloadFromJson(String str) => Payload.fromJson(json.decode(str));
...
factory Payload.fromJson(Map<String, dynamic> json) => Payload(
        copyright: json["copyright"],
        teams: List<TeamDetail>.from(
            json["teams"].map((x) => TeamDetail.fromJson(x))),
      );

working demo

full code

import 'package:flutter/material.dart';
import 'package:http/http.dart' as http;
import 'dart:convert';

Payload payloadFromJson(String str) => Payload.fromJson(json.decode(str));

class Payload {
  Payload({
    this.copyright,
    this.teams,
  });

  String copyright;
  List<TeamDetail> teams;

  factory Payload.fromJson(Map<String, dynamic> json) => Payload(
        copyright: json["copyright"],
        teams: List<TeamDetail>.from(
            json["teams"].map((x) => TeamDetail.fromJson(x))),
      );
}

class TeamDetail {
  TeamDetail({
    this.id,
    this.name,
  });

  int id;
  String name;

  factory TeamDetail.fromJson(Map<String, dynamic> json) => TeamDetail(
        id: json["id"],
        name: json["name"],
      );
}

void main() {
  runApp(MyApp());
}

class MyApp extends StatelessWidget {
  @override
  Widget build(BuildContext context) {
    return MaterialApp(
      title: 'Flutter Demo',
      theme: ThemeData(
        primarySwatch: Colors.blue,
        visualDensity: VisualDensity.adaptivePlatformDensity,
      ),
      home: MyHomePage(title: 'Flutter Demo Home Page'),
    );
  }
}

class MyHomePage extends StatefulWidget {
  MyHomePage({Key key, this.title}) : super(key: key);

  final String title;

  @override
  _MyHomePageState createState() => _MyHomePageState();
}

class _MyHomePageState extends State<MyHomePage> {
  int _counter = 0;
  Future<List<TeamDetail>> _future;

  Future<List<TeamDetail>> getTeamDetail() async {
    final response =
        await http.get('https://statsapi.web.nhl.com/api/v1/teams/1');

    if (response.statusCode == 200) {
      var payload = payloadFromJson(response.body);
      return payload.teams;
    } else {
      throw Exception("Failed to load");
    }
  }

  @override
  void initState() {
    _future = getTeamDetail();
    super.initState();
  }

  @override
  Widget build(BuildContext context) {
    return Scaffold(
        appBar: AppBar(
          title: Text(widget.title),
        ),
        body: FutureBuilder(
            future: _future,
            builder: (context, AsyncSnapshot<List<TeamDetail>> snapshot) {
              switch (snapshot.connectionState) {
                case ConnectionState.none:
                  return Text('none');
                case ConnectionState.waiting:
                  return Center(child: CircularProgressIndicator());
                case ConnectionState.active:
                  return Text('');
                case ConnectionState.done:
                  if (snapshot.hasError) {
                    return Text(
                      '${snapshot.error}',
                      style: TextStyle(color: Colors.red),
                    );
                  } else {
                    return ListView.builder(
                        itemCount: snapshot.data.length,
                        itemBuilder: (context, index) {
                          return Card(
                              elevation: 6.0,
                              child: Padding(
                                padding: const EdgeInsets.only(
                                    top: 6.0,
                                    bottom: 6.0,
                                    left: 8.0,
                                    right: 8.0),
                                child: Row(
                                  crossAxisAlignment: CrossAxisAlignment.start,
                                  children: <Widget>[
                                    Text(snapshot.data[index].id.toString()),
                                    Spacer(),
                                    Text(snapshot.data[index].name),
                                  ],
                                ),
                              ));
                        });
                  }
              }
            }));
  }
}