リクエストのバリデーション前に加工したい場合は、

Middleware機能を使うのが良いです。

$ php artisan make:middleware ConvertScoreToIntFilter

app/Http/Middleware/ConvertScoreToIntFilter.php

<?php

namespace App\Http\Middleware;

use Closure;

class ConvertScoreToIntFilter
{
    /**
     * Handle an incoming request.
     *
     * @param  \Illuminate\Http\Request  $request
     * @param  \Closure  $next
     * @return mixed
     */
    public function handle($request, Closure $next)
    {
        $request->merge([
            'score' => (int) str_replace(',', '', $request->score),
        ]);

        return $next($request);
    }
}

App/Http/Kernel.php

・・・

    protected $routeMiddleware = [
        'auth' => \App\Http\Middleware\Authenticate::class,
        'auth.basic' => \Illuminate\Auth\Middleware\AuthenticateWithBasicAuth::class,
        'guest' => \App\Http\Middleware\RedirectIfAuthenticated::class,
        'throttle' => \Illuminate\Routing\Middleware\ThrottleRequests::class,
        'admin' => \App\Http\Middleware\Adminpermission::class,
        'budgetFileter' => \App\Http\Middleware\ConvertCurrencyToIntFilter::class, ←●追加
    ];

・・・

App/Http/routes.php

    Route::post('/scoreInput', 'Admin\ScoreController@create')->middleware('scoreFileter')->name('scoreInput');