6dmongrel let in to accept piece of crust (8.5)t?c?o???p?a?e
15a holiday tha is extemely short taken by footballers (6)???s?a
16d shot adequate for approach )4.2.2) ?e?d?p?o
6d Tectonic plate (piece of [Earth's] crust) - anag (mongrel) 'let in to accept'
15a Fiesta - 'ie + s(hor)t' (that is + extreme letters of 'short', in) 'FA' (footballers)
16d Lead up to - 'lead' as shot - weight, ammo...