Times Cryptic 26293 Monday

[agsurfer]

5a Support back of ox, not rear of horse (6)

[dannyk13]

Any letters placed?

[agsurfer]

Thanks for responding. I have ?o?t?r

[dannyk13]

Only word I can come up with is foster but ca n't parse it

[mac44]

foster

[mac44]

of reversed + ste(e)r

[dannyk13]

got it Fo(of reversed) + steer(ox) - e(back of horse)

[writesbad]

back of = fo
ox, ste(e)r without rear of hors(e)

[agsurfer]

Thanks so much - it was my last clue.