Route::get('/events/{day}', 'FrontController@getEvents')->name('api.calendar');

public function getEvents($day)
{
return Event::with('user','gym')->select('id','title','start','user_id','gym_id')->get()
->groupBy(function($date) {
setlocale(LC_TIME, 'pl');
return Date::parse($date->start)->format('l');
});
}