We present the results of optical (R-band) photometric and polarimetric monitoring and Very Long Baseline Array imaging of the blazar S4?0954+658, along with Fermi γ-ray data during a multi-waveband outburst in 2011 March-April. After a faint state with a brightness level R?~ 17.6?mag registered in the first half of 2011 January, the optical brightness of the source started to rise and reached ~14.8?mag during the middle of March, showing flare-like behavior. The most spectacular case of intranight variability was observed during the night of 2011 March 9, when the blazar brightened by ~0.7?mag within 7?hr. During the rise of the flux, the position angle of the optical polarization rotated smoothly over more than 300°. At the same time, within 1σ uncertainty, a new superluminal knot appeared with an apparent speed of 19.0 ± 0.3c. We have very strong evidence that this knot is associated with the multi-waveband outburst in 2011 March-April. We also analyze the multi-frequency behavior of S4?0954+658 during a number of minor outbursts from 2008 August to 2012 April. We find some evidence of connections between at least two additional superluminal ejecta and near-simultaneous optical flares.
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