Agree with Dove, sun or/and wind damage. It's really common when hardening off as the soft leaves are just that 'soft'. New leaves will be tougher, don't worry about it too much.
In future years if you could build a 'hardening off stand' (it probably has a proper name) which is off the ground and has something like mesh or fleece to protect them from wind and direct sun, it can be avoided.
They are best off the ground because the air is much warmer at waist level.
Once they are in the ground, growth will be vigorous and the damaged leaves will be of little consequence.
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Gardening in Central Norfolk on improved gritty moraine over chalk ... free-draining.
In future years if you could build a 'hardening off stand' (it probably has a proper name) which is off the ground and has something like mesh or fleece to protect them from wind and direct sun, it can be avoided.
They are best off the ground because the air is much warmer at waist level.
Once they are in the ground, growth will be vigorous and the damaged leaves will be of little consequence.