Below is an instruction that describes a task. Write a response that appropriately completes the request.

### Instruction:
What match number has a ground of H and the opponent Chelsea under 18s?

### Inputs:
table_name: table, columns: ['Match', 'Date', 'Competition or tour', 'Ground', 'Opponent', 'Score1']

### Response:
SELECT AVG Match FROM table WHERE Ground = h AND Opponent = chelsea under 18s