diff --git a/api/teams/teams_service.py b/api/teams/teams_service.py
index 514e23a..186921f 100644
--- a/api/teams/teams_service.py
+++ b/api/teams/teams_service.py
@@ -241,11 +241,12 @@ def remove_team(team_id):
     if hackathon_event_id:
         hackathon_db_id = get_hackathon_by_event_id(hackathon_event_id)["id"]
         event_collection = db.collection("hackathons").document(hackathon_db_id)
-        event_collection_dict = event_collection.get().to_dict()
-        
-        # Remove the team from the hackathon event
+        event_collection_dict = event_collection.get().to_dict() or {}
+
+        # Remove the team from the hackathon event (tolerate docs with no
+        # `teams` key — same KeyError class as the queue_team linking bug)
         new_teams = []
-        for t in event_collection_dict["teams"]:
+        for t in event_collection_dict.get("teams") or []:
             if t != team_doc:
                 new_teams.append(t)
         
@@ -381,6 +382,25 @@ def edit_team(json):
             "team_id": team_id
         }
 
+
+def _append_team_to_hackathon(db, hackathon_db_id, team_ref):
+    """Link a team DocumentReference into hackathons/{id}.teams[].
+
+    Hackathon docs created through the admin UI may have no ``teams`` key at
+    all (not even an empty list); indexing it directly raised KeyError after
+    the team doc was already inserted, leaving the team orphaned from its
+    event (Sep 2026, test event fall-2026). Idempotent: an already-linked
+    team is not appended twice.
+    """
+    event_ref = db.collection("hackathons").document(hackathon_db_id)
+    event_dict = event_ref.get().to_dict() or {}
+    teams = list(event_dict.get("teams") or [])
+    existing_ids = {getattr(t, "id", None) for t in teams}
+    if getattr(team_ref, "id", None) not in existing_ids:
+        teams.append(team_ref)
+        event_ref.set({"teams": teams}, merge=True)
+    return teams
+
 def queue_team(propel_user_id, json):
     """
     Create a team and queue it for nonprofit pairing
@@ -539,17 +559,7 @@ def queue_team(propel_user_id, json):
 
     # Link the team to the hackathon event
     hackathon_db_id = get_hackathon_by_event_id(hackathon_event_id)["id"]
-    event_collection = db.collection("hackathons").document(hackathon_db_id)
-    event_collection_dict = event_collection.get().to_dict()
-
-    new_teams = []
-    for t in event_collection_dict["teams"]:
-        new_teams.append(t)
-    new_teams.append(new_team_doc)
-
-    event_collection.set({
-        "teams": new_teams
-    }, merge=True)
+    _append_team_to_hackathon(db, hackathon_db_id, new_team_doc)
 
     # Clear the cache
     logger.info("Clearing cache for event_id=%s doc_id=%s",
diff --git a/api/teams/tests/test_hackathon_team_linking.py b/api/teams/tests/test_hackathon_team_linking.py
new file mode 100644
index 0000000..3a7f7ad
--- /dev/null
+++ b/api/teams/tests/test_hackathon_team_linking.py
@@ -0,0 +1,77 @@
+"""
+Regression tests for the KeyError: 'teams' crash in team creation.
+
+Hackathon docs created through the admin UI can lack a ``teams`` key
+entirely. queue_team inserted the team doc, then did
+``event_collection_dict["teams"]`` and blew up, leaving the new team
+orphaned from its event (seen on test.ohack.dev with event fall-2026,
+Sep 2026). The linking now goes through _append_team_to_hackathon, which
+tolerates a missing key / missing doc and is idempotent.
+"""
+import os
+from unittest.mock import MagicMock
+
+os.environ.setdefault("ENVIRONMENT", "test")
+
+import api.teams.teams_service as svc
+
+
+def _db_with_hackathon(existing):
+    snapshot = MagicMock()
+    snapshot.to_dict.return_value = existing
+    event_ref = MagicMock()
+    event_ref.get.return_value = snapshot
+    collection = MagicMock()
+    collection.document.return_value = event_ref
+    db = MagicMock()
+    db.collection.return_value = collection
+    return db, event_ref
+
+
+def _ref(doc_id):
+    r = MagicMock()
+    r.id = doc_id
+    return r
+
+
+def test_links_team_when_hackathon_has_no_teams_key():
+    db, event_ref = _db_with_hackathon({"event_id": "fall-2026", "title": "ASU Fall"})
+    team = _ref("team-1")
+
+    result = svc._append_team_to_hackathon(db, "hack-doc", team)
+
+    assert result == [team]
+    written, kwargs = event_ref.set.call_args
+    assert written[0] == {"teams": [team]}
+    assert kwargs.get("merge") is True
+
+
+def test_appends_to_existing_teams_list():
+    existing_team = _ref("team-0")
+    db, event_ref = _db_with_hackathon({"teams": [existing_team]})
+    team = _ref("team-1")
+
+    result = svc._append_team_to_hackathon(db, "hack-doc", team)
+
+    assert result == [existing_team, team]
+    assert event_ref.set.call_args[0][0]["teams"] == [existing_team, team]
+
+
+def test_does_not_duplicate_an_already_linked_team():
+    team = _ref("team-1")
+    db, event_ref = _db_with_hackathon({"teams": [team]})
+
+    result = svc._append_team_to_hackathon(db, "hack-doc", team)
+
+    assert result == [team]
+    event_ref.set.assert_not_called()
+
+
+def test_tolerates_missing_hackathon_snapshot():
+    db, event_ref = _db_with_hackathon(None)
+    team = _ref("team-1")
+
+    result = svc._append_team_to_hackathon(db, "hack-doc", team)
+
+    assert result == [team]
+    assert event_ref.set.call_args[0][0] == {"teams": [team]}