diff --git a/src/Entity/Application.php b/src/Entity/Application.php
index 8805c53..a43fbaf 100644
--- a/src/Entity/Application.php
+++ b/src/Entity/Application.php
@@ -4,11 +4,13 @@ namespace App\Entity;
 
 use App\Entity\Traits\TimestampableEntity;
 use App\Repository\ApplicationRepository;
+use App\Validator\Constraints as AppAssert;
 use Doctrine\DBAL\Types\Types;
 use Doctrine\ORM\Mapping as ORM;
 use Symfony\Component\Uid\Uuid;
 
 #[ORM\Entity(repositoryClass: ApplicationRepository::class)]
+#[AppAssert\Application]
 class Application implements TimestampableEntityInterface
 {
     use TimestampableEntity;
diff --git a/src/Validator/Constraints/Application.php b/src/Validator/Constraints/Application.php
new file mode 100644
index 0000000..6984c0c
--- /dev/null
+++ b/src/Validator/Constraints/Application.php
@@ -0,0 +1,16 @@
+<?php
+
+namespace App\Validator\Constraints;
+
+use Symfony\Component\Validator\Constraint;
+
+#[\Attribute]
+class Application extends Constraint
+{
+    public string $message = 'Diese Bewerbung überlappt sich mit einem deiner bestätigten Einsätze';
+
+    public function getTargets(): array|string
+    {
+        return static::CLASS_CONSTRAINT;
+    }
+}
diff --git a/src/Validator/Constraints/ApplicationValidator.php b/src/Validator/Constraints/ApplicationValidator.php
new file mode 100644
index 0000000..3102c3d
--- /dev/null
+++ b/src/Validator/Constraints/ApplicationValidator.php
@@ -0,0 +1,65 @@
+<?php
+
+namespace App\Validator\Constraints;
+
+use App\Repository\DispositionRepository;
+use Symfony\Component\Validator\Constraint;
+use Symfony\Component\Validator\ConstraintValidator;
+
+class ApplicationValidator extends ConstraintValidator
+{
+    public function __construct(private readonly DispositionRepository $dispositionRepository)
+    {
+    }
+
+    public function validate(mixed $value, Constraint $constraint): void
+    {
+        /** @var \App\Entity\Application $application */
+        $application = $value;
+
+        $teamer = $application->getTeamer();
+
+        $assignment = $application->getAssignment();
+        $destination = $assignment->getDestination();
+
+        $applicationDateFrom = $destination->getDateFrom();
+        $applicationDateTo = $destination->getDateTo();
+
+        $qb = $this
+            ->dispositionRepository
+            ->createQueryBuilder('disposition')
+        ;
+
+        $conflictingCount = $qb
+            ->select($qb->expr()->count('disposition'))
+            ->innerJoin('disposition.assignment', 'assignment')
+            ->innerJoin('assignment.destination', 'destination')
+            ->where($qb->expr()->andX(
+                $qb->expr()->eq('disposition.teamer', ':teamer'),
+                $qb->expr()->orX(
+                    $qb->expr()->andX(
+                        $qb->expr()->gt('destination.dateTo', ':application_date_from'),
+                        $qb->expr()->lt('destination.dateTo', ':application_date_to'),
+                    ),
+                    $qb->expr()->andX(
+                        $qb->expr()->lt('destination.dateFrom', ':application_date_to'),
+                        $qb->expr()->gt('destination.dateFrom', ':application_date_from'),
+                    )
+                )
+            ))
+            ->setParameter('teamer', $teamer)
+            ->setParameter('application_date_from', $applicationDateFrom)
+            ->setParameter('application_date_to', $applicationDateTo)
+            ->getQuery()
+            ->getSingleScalarResult()
+        ;
+
+        if (0 < $conflictingCount) {
+            $this
+                ->context
+                ->buildViolation($constraint->message)
+                ->addViolation()
+            ;
+        }
+    }
+}
\ No newline at end of file
diff --git a/templates/forms.html.twig b/templates/forms.html.twig
index a541919..7f54cd3 100644
--- a/templates/forms.html.twig
+++ b/templates/forms.html.twig
@@ -24,7 +24,7 @@
 
 {%- block form_errors -%}
     {%- if errors|length > 0 -%}
-        <ul>
+        <ul class="pb-2">
             {%- for error in errors -%}
                 <li class="text-red-500">{{ error.message }}</li>
             {%- endfor -%}
diff --git a/templates/teamer/application/create.html.twig b/templates/teamer/application/create.html.twig
index 08f08af..7803636 100644
--- a/templates/teamer/application/create.html.twig
+++ b/templates/teamer/application/create.html.twig
@@ -16,6 +16,7 @@
             </h2>
             {% include '_partials/_assignment_requirements_info.html.twig' %}
             {{ form_start(form) }}
+            {{ form_errors(form) }}
             <div class="flex flex-col space-y-4 pb-8">
                 {% if form.pickup is defined %}
                     {{ form_row(form.pickup) }}