Since Tish'a B'av begins immediately after Shabbat, this year, this can present a shoe problem on Motza'ei Shabbat.
The conditions / halachot:
- One is not allowed to wear leather shoes on Tish'a B'Av.
- One is not allowed to prepare for after Shabbat on Shabbat, itself.
Assume that neighborhood shuls have Shabbat mincha which is followed by a shiur then Ma'ariv; and that they recommend that people bring their non-leather shoes to shul before Shabbat, and leave them in shul. Suppose someone cannot do this. (Say, he arrives for Fri. eve. davening immediately from work wearing his shoes, and can't get home to retrieve his non-leather shoes.)
He goes to shul for Shabbat mincha. He can't wear sneakers to shul, nor can he carry them (assume there's an eruv) since that is preparing for after Shabbat. In shul, at the start of Ma'ariv, he removes his shoes, so he's in his socks.
Walking home barefoot or in his socks could be harmful. The street frequently has broken glass shards, nails and other sharp objects which cannot easily be seen at night, and it's quite likely that the person may step on one of these and severely injure his foot. When shul is done, can he put on his leather shoes to walk home?