@using Telerik.DataSource

<TelerikGrid Data="@GridData"
             Pageable="true"
             Sortable="true"
             Groupable="true"
             FilterMode="GridFilterMode.FilterRow"
             OnStateInit="@( (GridStateEventArgs<Employee> args) => OnGridStateInit(args) )">
    <GridColumns>
        <GridColumn Field="@nameof(Employee.Name)" />
        <GridColumn Field="@nameof(Employee.Team)">
            <GroupHeaderTemplate>
                <table class="group-header-table">
                    <tr>
                        <td>Name content</td>
                        <td>Team content</td>
                        <td>Salary content</td>
                        <td>OnVacation content</td>
                    </tr>
                </table>
            </GroupHeaderTemplate>
        </GridColumn>
        <GridColumn Field="@nameof(Employee.Salary)" />
        <GridColumn Field="@nameof(Employee.OnVacation)" />
    </GridColumns>
</TelerikGrid>

<style>
    .k-grouping-row > .k-table-td:has(.group-header-table) {
        padding-top: 0;
        padding-bottom: 0;
        padding-right: 0;
    }

    .group-header-table {
        width: 100%;
        table-layout: fixed;
        border-spacing: 0;
    }
</style>

@code {
    private List<Employee> GridData { get; set; }

    private void OnGridStateInit(GridStateEventArgs<Employee> args)
    {
        var gridState = new GridState<Employee>();

        gridState.GroupDescriptors = new List<GroupDescriptor>();

        gridState.GroupDescriptors.Add(new GroupDescriptor()
        {
            Member = nameof(Employee.Team),
            MemberType = typeof(string)
        });

        args.GridState = gridState;
    }

    protected override void OnInitialized()
    {
        GridData = new List<Employee>();
        var rnd = new Random();

        for (int i = 1; i <= 20; i++)
        {
            GridData.Add(new Employee()
            {
                Id = i,
                Name = "Name " + i,
                Team = "Team " + (i % 4 + 1),
                Salary = (decimal)rnd.Next(1000, 3000),
                OnVacation = i % 3 == 0
            });
        }
    }

    public class Employee
    {
        public int Id { get; set; }
        public string Name { get; set; }
        public string Team { get; set; }
        public decimal Salary { get; set; }
        public bool OnVacation { get; set; }
    }
}