diff --git a/app/services/user_service.rb b/app/services/user_service.rb
new file mode 100644
index 0000000..fcbdf6e
--- /dev/null
+++ b/app/services/user_service.rb
@@ -0,0 +1,22 @@
+# frozen_string_literal: true
+
+class UserService
+  def initialize(user)
+    @user = user
+  end
+
+  def bet!(match, team)
+    validate_bet! match, team
+    @user.bets.create! match: match, team: team
+  end
+
+  private
+
+  def validate_bet!(match, team)
+    if team.nil?
+      raise 'Betting on no team in a playoff match is not supported' unless match.group_match?
+    else
+      raise 'The given team is not involved in the given match' unless match.teams.include? team
+    end
+  end
+end
diff --git a/spec/services/user_service_spec.rb b/spec/services/user_service_spec.rb
new file mode 100644
index 0000000..1711a36
--- /dev/null
+++ b/spec/services/user_service_spec.rb
@@ -0,0 +1,62 @@
+# frozen_string_literal: true
+
+RSpec.describe UserService do
+  before do
+    @user = create(:user)
+    @service = UserService.new @user
+    @team = create(:team)
+  end
+
+  describe '#bet!' do
+    context 'with an unrelated team' do
+      it 'throws an exception' do
+        expect do
+          @service.bet! create(:playoff_match), create(:team)
+        end.to raise_error('The given team is not involved in the given match')
+      end
+    end
+
+    context 'with an existing team' do
+      let(:match) do
+        create(:playoff_match, match_scores: [create(:match_score, team: @team)])
+      end
+
+      let(:bet) do
+        @service.bet! match, @team
+      end
+
+      it 'associates the bet with the given team' do
+        expect(@team.bets).to include(bet)
+      end
+
+      it 'associates the bet with the given match' do
+        expect(match.bets).to include(bet)
+      end
+
+      it 'associates the bet with the creating user' do
+        expect(@user.bets).to include(bet)
+      end
+    end
+    context 'without a team' do
+      context 'on a playoff stage' do
+        it 'throws an exception' do
+          match = create(:playoff_match)
+          match.match_scores << create(:match_score, team: @team)
+          expect do
+            @service.bet! match, nil
+          end.to raise_error('Betting on no team in a playoff match is not supported')
+        end
+      end
+
+      context 'on a group stage' do
+        it 'succeeds' do
+          match = create(:group_match)
+          match.match_scores << create(:match_score, team: @team)
+          bet = @service.bet! match, nil
+          expect(match.bets).to include(bet)
+          expect(@user.bets).to include(bet)
+        end
+      end
+    end
+  end
+end